Xonotic - Xonotic is a free (GPL), fast-paced first-person shooter that works on Windows, OS X and Linux.
Arma 2: Operation Arrowhead - Arma 2: Operation Arrowhead is a Tactical, First-person Shooter, Single and Multiplayer video game created by Bohemia Interactive Studios and published by 505 Games.
Quake - Quake is a series of first-person shooter video games released by id Software.
Call of Duty - Call of Duty is a first-person and third-person shooter series by Infinity Ward.
Counter-Strike - Counter-Strike is a PC-exclusive FPS video game developed by Valve Corporation.
S.T.A.L.K.E.R.: Shadow of Chernobyl - S.