OpenArena is a community-produced deathmatch FPS based on GPL idTech3 technology. There are many game types supported including Free For All, Capture The Flag, Domination, Overload, Harvester, and more. There are 17 unique player models to choose from and 12 weapons.
Basically Quake 3 for free with improved graphics.
But there's nothing basic about Q3, which still offers a genius fast-paced deathmatch mode, not unlike any present in more recent FPS.
Look no further if you are a fan of Quake & Unreal Tournament.