Borderlands - Borderlands is a science fiction first-person shooter with RPG elements made with cel-shaded...
Xonotic - Xonotic is a free (GPL), fast-paced first-person shooter that works on Windows, OS X and Linux.
Bulletstorm - In this sci-fi first person shooter, players take on the role of mercenary Grayson Hunt in an attempt to get off a hostile alien planet and get a little bit of vengeance along the way.
Quake - Quake is a series of first-person shooter video games released by id Software.
Urban Terror - Urban Terror started as a realism based "total conversion" mod for Quake III Arena.
Counter-Strike - Counter-Strike is a PC-exclusive FPS video game developed by Valve Corporation.