World of Padman (WoP) is an open source first-person shooter computer game

An online FPS based in the Wolfenstien universe with two teams Axis and Allies.

Warsow is a free standalone first person shooter game for Windows and Linux. It is based on the Qfusion 3D engine (a modification of the Quake 2 GPL engine), and aimed on the competitive scene, or the e-sports community.

a first-person shooter computer game that uses the Ageia PhysX engine.

War Rock is a multiplayer online first-person shooter available free for download

Urban Terror can be described as a Hollywood tactical shooter; somewhat realism based, but the motto is "fun over realism". This results in a very unique, enjoyable and addictive game.

Tribes 2 (commonly abbreviated to T2) is a sci-fi first-person shooter (FPS) computer game based in the fictional Earthsiege universe

Tremulous is a free, open source game that blends a team based FPS with elements of an RTS. Players can choose from 2 unique races, aliens and humans.

Set in 2040, gamers participate in the conflicts of tomorrow in urban and open field infantry combat.

QUAKE LIVE is an innovative multiplayer game experience from id Software - the creators of DOOM and QUAKE