Xonotic - Xonotic is a free (GPL), fast-paced first-person shooter that works on Windows, OS X and Linux.
Quake - Quake is a series of first-person shooter video games released by id Software.
Counter-Strike - Counter-Strike is a PC-exclusive FPS video game developed by Valve Corporation.
AssaultCube - AssaultCube is a FREE multiplayer first-person shooter game. Taking place in realistic environments, with fast, arcade gameplay, it's addictive and fun!
Call of Duty - Call of Duty is a first-person and third-person shooter series by Infinity Ward.
Overwatch - Stylized team-based FPS