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).
WG Realms 2: Siege Breaker
WG Realms 2: Siege Breaker is an action packed total conversion of Duke Nukem 3D, by William Gee, Dan Gaskill, and Cage. You don't need Duke 3D for this; just download.
White is an extremely original free FPS game that explores both the inherent violence of the genre as well as the players’ creativity. Your talent will determine the outcome...
Wolfenstein: Enemy Territory
Wolfenstein: Enemy Territory is a free, stand-alone, downloadable multiplayer game in which players wage war as Axis or Allies in team-based combat.
World of Padman
World of Padman made the change from a mod for Quake 3 Arena. It is available for free and features 7 game types, 12 maps, 6 player characters, own music, and a lot of fun.
Xonotic is an open source FPS that follows in the footsteps of popular free-to-play game~Nexuiz. This is an ambitious multiplayer shooter that includes the usual singleplayer...
Zombie Master is a free to download and play multiplayer Half-Life 2 modification set in a world where a zombie apocalypse is happening. You play as one of the survivors...