Sniper Elite V2 - Sniper Elite V2 is a Fantastic, Action-Adventure, Stealth, Co-op, WWII, First and Third-person Shooter, Tactical, Single and Multiplayer video game created and published by Rebellion.
Xonotic - Xonotic is a free (GPL), fast-paced first-person shooter that works on Windows, OS X and Linux.
S.T.A.L.K.E.R.: Shadow of Chernobyl - S.
Quake - Quake is a series of first-person shooter video games released by id Software.
Arma II - Arma II is an Awesome, Action-Adventure, Military-themed, FPS (First-person Shooter), Tactical, Co-op, Strategy, Single and Multiplayer Simulation developed and published by Bohemia Interactive.
Counter-Strike - Counter-Strike is a PC-exclusive FPS video game developed by Valve Corporation.