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

An open-source content package for Quake III Arena licensed under the GPL, effectively creating a free stand-alone game. You do not need Quake III Arena to play this game.

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.

.kkrieger (from Krieger, German for warrior) is a first-person shooter computer game created by the German demogroup .theprodukkt and won first place in the 96k game competition at Breakpoint in April 2004.

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.

FEAR Combat is the multiplayer part of FEAR that has been released for free.

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

America's Army is a video game owned by the United States Government and offers accurate FPS action

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

A GPL first-person shooter by Alientrap Software. with nine weapons, 24 official maps and over 240 community created maps, as well as 15 player models.