Video game whose source code is open-source software
An open-source video game, or simply an open-source game, is a video game whose source code is open-source. They are often freely distributable and sometimes cross-platform compatible.
In general, open-source games are developed by relatively small groups of people in their free time, with profit not being the main focus. Many open-source games are volunteer-run projects, and as such, developers of free games are often hobbyists and enthusiasts. The consequence of this is that open-source games often take longer to mature, are less common[2] and often lack the production value of commercial titles.[3] In the 1990s a challenge to build high-quality content for games was the missing availability or the excessive price for tools like 3D modeller or toolsets for level design.[4]
In recent years, this changed and availability of open-source tools like Blender, game engines and libraries drove open source and independent video gaming.[5]FLOSS game engines, like the Godot game engine, as well as libraries, like SDL, are increasingly common in game development, even proprietary ones.[6] Given that game art is not considered software, there is debate about the philosophical or ethical obstacles in selling a game where its art is proprietary but the entire source code is free software.[7][8][9]
Some of the open-source game projects are based on formerly proprietary games, whose source code was released as open-source software, while the game content (such as graphics, audio and levels) may or may not be under a free license.[10] Examples include Warzone 2100 (a real-time strategy game)[11] and Micropolis (a city-building simulator based on the SimCity source code). Advantage of such continuation projects is that these games are already "complete" as graphic and audio content is available, and therefore the open-source authors can focus on porting, fixing bugs or modding the games.
In a 2004 article, Adam Geitgey questioned the compatibility of the open-source culture with respect to the game development process. He suggested that perceived open-source development advantages do not work for games because users move on to new games relatively quickly and so do not give back to the project. Geitgey further noted that music and art development is not built up from the work of others in the same way that coding would be. He argued that high quality art content is required, which is typically produced commercially by paid artists. While Linux operates on the open-source philosophy, this may not benefit game development.[12]
As of September 2015, the Steam gaming service has 1,500 games available on Linux, compared to 2,323 games for Mac and 6,500 Windows games.[13][14][15]
Just as in most other forms of software, free software was an unconscious occurrence during the creation of early computer games, particularly for earlier Unixgames. These are mostly arcade conversions, parlour games, and text adventures using libraries like curses.[16][17] A notable example of this is the "BSD Games", a collection of interactive fiction and other text-mode titles.[18][19] Game fan communities such as the modding community do include some aspects of free software, such as sharing mods across community sites, sometimes with free to use media made for the modification.[20]
The Freeciv project was started in 1995 and gave rise to another new style of free game development. Similar to the cooperative nature of the Linux kernel development, Freeciv was extended by many volunteers, rather than only one or two authors.[43] It had started out as a small university student project but then branched out into its current form and is still being developed today. Freeciv also proved to be one of the earliest very popular free software games, and was among the first to be included with Linux distributions, a system commonly known now as a source of peer review or selection of quality for free gaming projects. Magazines, news sources and websites have also started noting free games, often in listings.[44][45][46][47]Freeciv and other archetypes have led to the development of many other clones of popular proprietary games.[48][49]Lincity was also started in 1995, despite there having been a Unix version of its namesake officially released by DUX Software in 1990.[50]
Proprietary games such as Doom and Descent brought in the age of three-dimensional games in the early to mid 1990s, and free games started to make the switch themselves. Tuxedo T. Penguin: A Quest for Herring by Steve Baker, a game featuring the Linux mascot Tux and introducing the PLIB library, was an early example of a three-dimensional free software game.[54] He and his son Oliver would later create other popular 3D free games and clones such as TuxKart and contribute to those by other developers such as Tux Racer. BZFlag pre-dates all of these, inspired by Battlezone and started in 1992 and released in 1993. FlightGear, YSFlight, ACM,[55] and GL-117[56] are also good examples of original 3D games, first started in 1997, 1999 and 2003 respectively (and the latter eventually forked as Linux Air Combat[57]), especially noting that they are not first-person shooters but flight simulators; Danger from the Deep meanwhile simulates submarines.[58]
The OpenGL specification provided a foundation for hardware acceleration since 1992, primarily through the free Mesa implementation since 1995, and later complimented by Vulkan since 2016.[59] The Direct3D API has also been made available on free operating systems via compatibility layers such as WineD3D and DXKV. The Glide API was also made open source following the dissolution of 3dfx in 2002.
Frozen Bubble, originally a clone of Puzzle Bobble, has become a classic known for its addictive gameplay and winner of many Linux Journal Reader's Choice Awards.[267] These games and others have also helped expand the prevalent Tux genre which started with titles and like A Quest for Herring and are related to the activist content of games like XBill. As well as ground up clones,[268] open source re-implementations of various proprietary games have become increasingly common, which utilize the original game data.[269]
The Stratagus project began as an attempt to recreate the proprietary Warcraft II engine, under the name FreeCraft. Blizzard Entertainment sent a cease and desist letter in 2003 over the use of the name "craft" in comparison to Warcraft and StarCraft.[414] Though the earlier free software strategy game CRAFT: The Vicious Vikings shared the name "craft" without controversy.[415] With the new, legally inoffensive name Stratagus and the old FreeCraft assets renamed Aleona's Tales, the team began work on a new strategy game called Bos Wars.
Development on this game still continues, as well as the modern Warcraft II port Wargus. Other games branched out of the engine project as well such as the Battle for Mandicor and Astroseries projects, the StarCraft port attempt Stargus, and most recently Wyrmsun.[416] After the Stratagus example, other real-time strategy games were developed, such as Globulation 2, which experiments with game management mechanics, the similarly experimental Liquid War, mutliplayer military game TUD,[415] the claymation based Dark Oberon,[417] and the 3D projects 0 A.D. (a former freeware project), Boson,[418]Battles of Antargis,[419]Spring and Glest.[344]
Despite its initial roots as individual projects, the free software gaming scene has been becoming progressively more organized. The roots of this even go back as far as the games created for the GNU Project and to the original larger-scale free software projects like Freeciv. Still, for the most part free game development had very little organization throughout its history.[462] Popular games were generally separate efforts, except for instances of people working on them known for other projects such as Ingo Ruhnke (Pingus), Bill Kendrick (SuperTux) and Steve Baker (TuxKart).[463] Games were commonly found in directories such as The Linux Game Tome[464] and Freshmeat[465] and hosted on sites like SourceForge[466][467] and GNU Savannah, but they were largely only ever brought together in the form of disorganized lists.[468][469][470][471] Other projects and games existed purely on isolated personal or project websites, often unknown and ignored.[472]
The launch of the GNOME and KDE desktop projects in the late 1990s organized application and, to a certain extent, game development. Both attempts to create a more usable Linux desktop attracted volunteers to make utilities to that end. These programs included games, mostly recreations of small games like Minesweeper or Solitaire that come with Microsoft Windows, arcade classics and the like, games from combined sets such as Microsoft Entertainment Pack, and occasionally original ideas.[473]
The Battle for Wesnoth project was started in 2003 and quickly became popular to both players and editors. It also showcased some new ideas when it came to free game development.[488] Like Freeciv before it, it utilized the efforts of the gaming and free software community and their code, levels and artwork contributions but it also accepted storyline contributions and ideas for the game's entire fictional universe. The game's canon is maintained through review and discussion over which submitted campaigns become official, thus setting up a model for community input and organized results.[489] This helped the game grow in scale and popularity to the point of being almost saga-like in scope. In addition, the project is worked on by many well-known free programmers, artists, designers and musicians such as the co-founder of the Open Source InitiativeEric S. Raymond,[490] and Linux kernel hackerRusty Russell.[491][492]Vega Strike has similarly allowed its community to expand the game and the surrounding lore while maintaining canon consistency.[493] The Wesnoth developers also worked on Frogatto & Friends, which features a free engine but mostly proprietary game data.
The general lack of unity and organization has created and continues to generate some controversy among the free software community, with problems of "reinventing the wheel" by making similar clones, games and multimedia resources being cited as a notable problem to free game development.[494] This is especially taking up more notice as other problems are corrected, such as a lack of tools, libraries, artists and coders. A more central knowledge bank, texture library, and discussion area had been lacking.[495]
Traditionally free software video games were developed as individual projects, some small scale and others larger scale.[215] Programmers and other developers did often work on other projects, but the whole system was very unlinked.[496] More recently free software development teams have started appearing, groups that function like software companies and create multiple pieces of work. Examples include the developer Parallel Realities, which have released the games Project: Starfighter, The Legend of Edgar, Blob Wars: Metal Blob Solid, as well as its sequel, Blob Wars: Blob and Conquer.[497]
The Linux Game Tome "Game of the Month" team was an open group of game developers that revamp old free software games. Some examples include the transformation of TuxKart into the more modern SuperTuxKart, work on Pingus and SuperTux, and Lincity-NG, an updated version of Lincity with superior graphics.[498] A more recent project with similar goals exists called LibreGames, which has worked on Jump 'n Bump, OpenAlchemist and FreeTumble and JAG.[499] Identical Software has also worked to modernize various libre games, including Ostrich Riders, Shippy 1984, OpenAlchemist, Mojotron, Seahorse Adventures, Thrust, and Mari0.[500][501]
PlayPower is a non-profit organization founded in 2008 designed to create free educational computer software for low income families in India and other developing countries. The Tux4Kids initiative also maintains various educational games featuring the child-friendly Tux character such as Tux Paint, Tux, of Math Command, Tux Typing and related efforts.[503] The GCompris suite is also available from KDE,[504] and the activity centre Childsplay is also available.[505]
GitHub, GitLab and Gitea now hosts a significant number of free and open-source games.[515][516][517]
The itch.io service is also a host for many open source games, and also features an open source client.[518] The same is true for competitor Game Jolt,[519] and was also the case for former distributor Desura.[520] A number of open source games have even been made available on Steam.[521][522][523] Many free software games are also available from Flathub and Snap.
^Stallman, Richard. "Linux and the GNU System". GNU Project. Archived from the original on 19 March 2017. Retrieved 20 July 2022. Some of our system components, the programming tools, became popular on their own among programmers, but we wrote many components that are not tools. We even developed a chess game, GNU Chess, because a complete system needs games too.
^Petersen, Mickey (24 May 2022). "Fun and Games in Emacs". Mastering Emacs. Retrieved 18 March 2023.
^Heng, Christopher (3 October 2022). "Free Game Engines, Programming Libraries and Source Code". thefreecountry.com. Retrieved 10 February 2023. This is a 3D game engine for Windows first person shooter (FPS) games. It uses OpenGL for hardware accelerated transformation and lighting and DirectSound for music and 3D sound effects. The engine supports particle effects, shaders, glow maps, volumetric fog and explosions, stencil shadows, chrome maps, weather effects, damage decals, etc. It has support for complex 3D models and a wide variety of generic weapon types (melee weapons like a fist, projectile weapons like a laser blaster, exploding projectile weapons like a rocket launcher, instant hit weapons like a pistol, beam weapons like a rail gun, grenades, and shotgun) that can be customised. It also has a scripting engine with a GUI interface that lets you create scripts without learning the scripting language. The engine comes with a variety of tools, including a level editor, a model editor and an episode editor. Also included are some freeware games. The engine is released under the GNU General Public License.
^Cocchiaro, Nicola. "Alpha Shooter - A 3D sci-fi First Person Shooter". SourceForge. Retrieved 17 March 2023. Alpha Shooter is a 3D FPS game with a sci-fi setting, developed by Nicola Cocchiaro and released under the GNU General Public License. It is currently written in C++ and uses its own reusable game engine, named Neutron. The game (and its engine) will evolve to include simulated physics and artificial intelligence, a scripted storyline, involving music and sound effects and more.
^Olakunle, Olanrewaju (5 February 2022). "20 Best Programming Languages for Game Development". Dunebook. Retrieved 25 March 2023. Niklaus Wirth is the creator of this language. A lot of game engines like Mingro, Nxpascal, Castle game engines are written in Pascal language.
^Gutekanst, Stephen (10 April 2021). "My game development journey". Hexops. Retrieved 25 March 2023. I spent the next 4 years of my life, almost 100% full-time working on Azul3D, a game engine in Go - and spent only minimal time attending online community college on the weekends.
^"Hedged 1.2". Internet ArchiveCommunity Software. 31 May 2021. Retrieved 25 March 2023. It was written in Gambas 3.15.2 and uses Qt 5 for interfaces, SDL 2 for audio and OpenGL 2.1 for rendering. Created in six days, it features a beta version of the second revision of the PS Tech engine.
^Saqib, M. (21 December 2021). "Delta Engine – 2D and 3D Application Engine written in C++". MYCPLUS. Retrieved 26 March 2023. Furthermore, the Delta Engine can be easily transformed between Java C++, C#, Objective-C and JavaScript. This makes it ultimately a cross platform Game Engine.
^lululaglue (24 June 2009). "Entretien avec l'équipe de Smokin'Guns". Jeuxlinux (in French). Archived from the original on 19 March 2021. Retrieved 5 January 2010. Alas, artists are always conservative for their creations. For me, the most important thing was to have the code under a free license... it always leaves the opportunity for other creators to take over the game with new data, but it's a hell of a job! Honestly, I am for free, but free is not always the panacea and our creators do not want to find their babies anywhere without their consent. Anyone today who wants to offer free content to replace cc licensed content with better quality will be welcomed with open arms as a possible future team member :D And anyone who wants to use our content for another project is safe ask permission on our forum.
^Wuttke-Hohendorf, Nikolai (3 October 2023). "Duke Nukem 1+2 Remastered". Rigel Engine. Retrieved 12 November 2023. If you've seen or used RigelEngine before, some of the new features will sound familiar – the project is in fact based on RigelEngine.
^Whitehead, Jim (29 October 2009). "Landscape of open source games". Expressive Intelligence Studio Blog. Retrieved 17 September 2023. One was how many open source game-creation systems I found (4, more than the zero I expected). These are Game Editor (2d with export to some mobile devices), Construct (2d, some 3d), Novashell (2d), and Sandbox (3d).
^Wood, Evelyn (6 October 2016). "Succeeding MegaZeux". fuzzy notepad. Retrieved 14 February 2023.
^van de Donk, Joris (2012). "FreeGish". Mooses.nl. Retrieved 12 February 2023.
^ abGleason, Alex (26 September 2018). "Libre Game Spotlight, idea for a video series about libre games". Retrieved 12 February 2023. Hexoshi – this game's resemblance to Metroid makes it relatable to gamers. The game's tight controls and solid gameplay may be a good stepping stone for people.
^Zymaris, Con (July 2001). "The Open Source Lucky Dip". AUUGN. Australia: AUUG. Retrieved 6 February 2023. Written by David Jaffe, Dave Gnukem is a 2D scrolling platform game, similar to Duke Nukem 1. It includes a sprite and level editor. It uses GGI and thus runs on the console as well as X, windowed or fullscreeen. It also runs on Windows, using DirectX. Download it and blow yourself away
^"Formido". The Linux Game Book. Retrieved 9 December 2023.
^"Violetland". LinuxLinks. Retrieved 9 December 2012.
^Nguyen, Binh. Linux Dictionary. p. 1095. An improved version of Paradroid - a strategic shoot-em up. You are a droid out to save the universe. To do this, you must do more than simply blasting everything in sight - you have to transfer to better droids in order to conquer more advanced droids, and go through walls to reach parts other droids cannot reach.
^"Escape". The Linux Game Book. Retrieved 9 December 2023.
^gameblabla (8 November 2016). "ToaruOS - Unix-like "hobby" operating system". codewalr.us. Retrieved 25 April 2023. I ported Helicopters, one of my games, just to show you how easy you can port games to it.
^Saeki, Takaya (4 October 2020). "How we ran a Unix-like OS (Xv6) on our home-built CPU with our home-built C compiler". Fuelled by Coffee. Retrieved 25 April 2023. However, some teams put more energy into doing fun such as running games or playing music by connecting a speaker with their CPU. Group 6, to which I belonged, was a group of such people who loved entertainment, and we decided to run an OS as our team goal.
^Larabel, Michael (13 February 2024). "The Current State & Plans For Porting Linux/BSD Software To Redox OS". Phoronix. Retrieved 24 February 2024. While not yet having accelerated graphics and their Wayland support is still some ways out, they have ported some games/emulators to Redox OS already like DOSBox, Neverball, OpenTTD, ScummVM, 2048, and others.
^Pendleton, Bob. "Game Programming with the Simple DirectMedia Layer". ACM Digital Library. SDL officially supports Linux, Windows, BeOS, Mac OS, Mac OS X, FreeBSD, OpenBSD, BSD/OS, Solaris and IRIX. SDL also works with Windows CE, AmigaOS, Atari, QNX, NetBSD, AIX, Tru64 UNIX and SymbianOS. However, those OSes are not yet officially supported. This means if you write your application using SDL, you can port it with minimal rework to all those OSes. SDL provides a portable way to write games and multimedia applications on every major OS currently in use.
^Baker, Jason (21 July 2015). "Linux game review: OpenTTD". Opensource.com. Retrieved 4 March 2023. While it runs on a number of platforms (including some surprising ones, like ReactOS, BeOS, and OS/2), the Linux installation of OpenTTD is quick and easy.
^"History - Year 2000". Stendhal project. Retrieved 4 March 2023. Also a BeOS version was released and hence Arianne was one of the first BeOS open source games.
^Zinoune, M. (2011). "Let 'The Battle for Wesnoth' continue with latest version 1.9.9". Unixmen. Retrieved 4 March 2023. It is multi-platform game, which is easy to install on Windows to MacOSX and open source platform such as FreeBSD, Open BSD, NetBSD and now historic BeOS.
^Williams, Al (3 May 2017). "Your Next Desktop… QNX?". Hackaday. Retrieved 5 March 2023. The rest of the adventure went fairly well. He managed to build SDL and port over some games.
^Petkauska, Vilius (28 September 2021). "Forget Windows, Apples, and Penguins: enter a world of 'lost' OSs". CyberNews. Impressively, MenuetOS is no thought experiment. To illustrate the point, the operating system ships with shareware versions of legendary games 'Quake' and 'Doom'.
^Dominikowski, Tomasz (4 September 2006). "SkyOS Beta Build 6179 Released". OSNews. Retrieved 24 April 2023. This new build also includes new ports, such as Quake III, Python, SDL with OpenGL support, and much more.
^Whitham, Jack (6 July 2015). "Porting third-party programs to TempleOS". Retrieved 25 March 2023. Without graphics support, the proof-of-concept application is quite limited in what it can do. I therefore chose to port "frotz". This is an interpreter for Z-machine games. The system requirements are minimal, but it can be used to play perhaps thousands of "interactive fiction" (text adventure) games.
^"SymbOS - A rather impressive Z80 multitasking operating system gets a new release". Indie Retro News. 7 January 2022. Retrieved 25 April 2023. You can not only play the latest 8bit version of Doom converted by Prodatron, but many other games such as Sakoban, 2048 and yes even Flappy Bird via this graphically impressive Z80 operating system.
^Styger, Erich (2 December 2018). "Playing Zork with FreeRTOS on ARM in three different Ways". MCU on Eclipse. I started my port of Zork for the NXP FRDM-K64F board using the port from Thomas Shane. You can find my port for the FRDM-K64F on GitHub (links at the end of this article). It should be fairly simple to port it to any other board. The game code has been converted to C using a converter (so the code looks rather ugly with lots of goto statements).
^"Simutrans: Free and Open Source Transport Simulation Game". From Linux. 13 April 2022. Retrieved 4 March 2023. Simutrans is an open source simulation game under the Artistic License 1.0 for Windows, AmigaOS, BeOS, Mac OS X and Linux that focuses on freight, passenger, mail and energy transport.
^"Games". MorphOS Library. 20 December 2009. Retrieved 4 March 2023. Many open source games have been ported to MorphOS, including several commercial games whose sources have been released, like id Software masterpieces Wolfenstein 3D, Doom, Doom II, Quake, Quake II and Quake III.
^Holwerda, Thom (19 March 2007). "Review: Zeta 1.5". OSNews. Retrieved 1 May 2023. Magnussoft also included a few emulators (including graphical frontends) in this release, two of which I want to highlight: DOSbox and Qemu. Using the DosBox emulator, I was able to play some old DOS games (Keen!), even though I had to edit the DOSbox config file in order to get some decent performance. The QemuVM frontend had problems in that it would not work correctly when using physical disks instead of image files.
^Petkauska, Vilius (28 September 2021). "Forget Windows, Apples, and Penguins: enter a world of 'lost' OSs". CyberNews. Kolibri features a rich set of applications that include a word processor, image viewer, graphical editor, web browser, and well over 30 exciting games," states the authors of the operating system.
^Wilson, Hamish (12 September 2022). "Building a Retro Linux Gaming Computer - Part 18: Run Away and Join the Circus". GamingOnLinux. Retrieved 4 March 2023. Bill Kendrick has also created a number of other arcade conversions, edutainment, and experimental software toys which he ports to the widest possible range of platforms, all of which can still be found on the New Breed Software website.
^Kendrick, Bill. "Welcome". New Breed Software. Retrieved 4 March 2023.
^Wilson, Hamish (12 September 2022). "Building a Retro Linux Gaming Computer - Part 18: Run Away and Join the Circus". GamingOnLinux. Retrieved 2 February 2023. He is most famous for starting work on the platformer SuperTux and crafting the drawing program Tux Paint, helping to popularize Tux as a gaming icon with others in the Tux4Kids initiative, all alongside the work of people like Steve Baker and Ingo Ruhnke.
^Gasperson, Tina (16 December 2004). "Site review: Linux Game Tome". Linux.com. Retrieved 19 February 2023. LGT sponsors annual awards where members of the site vote for the best free and non-free games of the year. A "miscellaneous" category also singles out the best sounds, emulators, toys, and the most promising Linux game project. The current top free game is Frozen Bubble, and the favorite commercial game is Quake 3 Arena.
^Bar, Joe (21 July 2000). "Procrastinate with these Linux games". CNN. Archived from the original on 7 October 2009. Retrieved 19 February 2023. Freshmeat was the focal point of my search. With over 300 games listed in the X11 section and 200 in the console section, it provided more games than I could possibly evaluate. Naturally, since I want instant gratification of my need for fun, I tended to look only at those with stable releases.
^Kenlon, Seth (26 February 2022). "My favorite casual games to play on Linux". Opensource.com. Retrieved 1 May 2023. These aren't by any means the only two games from the KDE project. There are many others, including card games, tile games, and arcade games. The nice thing about the KDE Games package is that they contain games you're happy to walk away from at a moment's notice, and they only require about a fourth of your attention. I use these to kill time while compiling code. Sometimes I don't get a full game in, but I always appreciate the subtle shift in mental gears.
^Mills, Ashton (17 September 2007). "Open Source Challenge part 9: Gaming". APC. Archived from the original on 16 January 2010. Retrieved 20 July 2022. Thanks to open source, there are actually quite a few fun and free games to download and for which the Ubuntu repositories have a fine selection. From the Applications > Add/Remove menu there's a whole range of games from the basic classics like Nethack and Frozen Bubble through to 3D accelerated gems like Chromium and Neverball. I played all of these. And then I played some more. And then some more. How do they make these so damn addictive? They're not blockbusters, but they beat the pants off the free games bundled in Windows, and will keep you occupied for many hours longer. Good deal for the price point.
^Lucas, Michael (22 March 2001). "FreeBSD Gaming". ONLamp. Archived from the original on 20 January 2018. Retrieved 9 July 2023. If you're running KDE or Gnome, you already have a few simple games installed. I'm not a fan of either desktop -- both strike me as bloated and obtuse -- but their games packages are a nice way to pick up a dozen simple favorites such as Solitaire, Asteroids, and Tetris.
^"Solaris 9 GNOME 2". Toasty Tech. Retrieved 26 April 2023. The desktop includes a number of games that typically come with GNOME.
^JackS (1 August 2005). "Please Only Put "Authoritative" Data into the Wiki". Vega Strike. Retrieved 9 December 2023. If one wishes to contribute, or is dismayed at the absence of any piece or pieces of data, one should ask, query, inquire - that is to say, communicate - via appropriate channels. We have a wiki because we are engaged in a collaborative attempt at documenting and presenting data that has been generated concerning the VS universe, and because we, as a community, would like to think we're up to developing a culture where that is a pleasant venture.
^"Highly Addictive Puzzle/Arcade Games for Linux". TechSource. 2 May 2008. Retrieved 4 February 2023. Work on [Pingus] began in 1998. This game is the first Game of the Month by The Linux Game Tome, which has revamped such games as SuperTux, Super TuxKart, and Lincity. The first post-GotM version 0.6 was released in 2003 for Linux featuring new levels and a level editor.
^Whitehead, Jim (29 October 2009). "Landscape of open source games". Expressive Intelligence Studio Blog. Retrieved 17 September 2023. A disappointment was the state of open content sharing. While some sites, like OpenGameArt and New Grounds provide tagging with a Creative Commons license, far more common are sites like Google's 3D Warehouse that have site-specific terms of use, and provide no ability for artists to indicate they are willing to share their work via Creative Commons or an open source license.