Nexuiz
Qtracker v.4 92
Qtracker supports over 100 of the most popular multiplayer games, and is actively supported with regular updates If you've ever played a multiplayer game on your PC, the in-game server browser has probably left you wanting more.
Xonotic v.0.6.0
Xonotic is a free (GPL), fast-paced first-person shooter that works on Windows, OS X and Linux.