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Athena framework is software[1] based on the common Gaudi framework used for the Atlas experiment, the largest, general-purpose particle detector experiment at the Large Hadron Collider (LHC), a particle accelerator at CERN (the European Organization for Nuclear Research) in Switzerland[2]. The Athena is also used by other experiments at CERN, such as LHCb and FCC experiments.
Athena code is hosted in the CERN GitLab [3] service where the repository owned by the atlas user plays a special role as the repository from which all production releases will be built. In the ATLAS development workflow this repository is also the merge target for developments from individual users or groups. There is much more information about the development workflow in the ATLAS git development tutorial.