OpenArena is a community-produced deathmatch FPS based on GPL idTech3 technology.

GitHub - OpenArena/engine OpenArena modifications to the ioquake3 engine
GitHub - undeadzy/openarena_engine Unofficial port of OpenArena 0.8.8 client/server to the latest ioquake3 source code
GitHub - everettcaleb/openarena Open Arena game based on IOQuake3
GitHub - everettcaleb/openarena-engine Slightly modified IOQuake3 used in Open Arena