Xonotic - Xonotic is a free (GPL), fast-paced first-person shooter that works on Windows, OS X and Linux.
PlaneShift - PlaneShift is a Free Massively Multiplayer Online Role Playing Game. Free?
Counter-Strike - Counter-Strike is a PC-exclusive FPS video game developed by Valve Corporation.
Rift: Storm Legion - Rift: Storm Legion is an Action, Fantasy-based, massively Multiplayer Online, and Role-playing video game developed and published by Trion Worlds.
Quake - Quake is a series of first-person shooter video games released by id Software.
Wizardry Online - Wizardry Online is an Action, Free-to-play, and MMORPG video game created by GameSpot and published by Sony Online Entertainment.