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.
It's pretty much a Quake rip-off... But that's why I like it, Also because it's free. The CPU's talking trash is a nice touch. Also there's a furry model... So you know...