Lunacraft - Lunacraft focuses on Endless Creativity and Exploration elements.
Xonotic - Xonotic is a free (GPL), fast-paced first-person shooter that works on Windows, OS X and Linux.
Ace of Spades: Battle Builder - Say hello to the creative shooter. Create your battleground, destroy it, then create it again.
Counter-Strike - Counter-Strike is a PC-exclusive FPS video game developed by Valve Corporation.
Roblox - Reimagining the way people come together.
Quake - Quake is a series of first-person shooter video games released by id Software.