Xonotic - Xonotic is a free (GPL), fast-paced first-person shooter that works on Windows, OS X and Linux.
ZombiU - Zombi U is an Addictive, Action-Adventure, Horror-Survival, FPS (First-person Shooter), Single and Multiplayer video game developed and published by Ubisoft.
Unreal Tournament - Unreal is a series of first-person shooter video games developed by Epic Games.
Quake - Quake is a series of first-person shooter video games released by id Software.
State of Decay - State of Decay mixes the open world genre using a zombie out-break to create among the largest and most remarkable games in the genre to date.
Counter-Strike - Counter-Strike is a PC-exclusive FPS video game developed by Valve Corporation.