Xonotic - Xonotic is a free (GPL), fast-paced first-person shooter that works on Windows, OS X and Linux.
Alien Shooter 2: Reloaded - Alien Shooter 2: Reloaded combines the elements of Role-playing, Top-down, Action, and Shooter.
Quake - Quake is a series of first-person shooter video games released by id Software.
Alien Shooter - Alien Shooter is an Engaging, Action, Isometric, Role-playing, Top-down, and Single-player Shooter video game created and published by Sigma Team Inc.
Counter-Strike - Counter-Strike is a PC-exclusive FPS video game developed by Valve Corporation.
Alien Swarm - Alien Swarm is a F2P, Co-op, Alien, Top-down Shooter, Single and Multiplayer video game developed and published by Valve Corporation.