Call of Duty - Call of Duty is a first-person and third-person shooter series by Infinity Ward.
Xonotic - Xonotic is a free (GPL), fast-paced first-person shooter that works on Windows, OS X and Linux.
Arma - Experience true combat gameplay in a massive military sandbox.
Unreal Tournament - Unreal is a series of first-person shooter video games developed by Epic Games.
War Thunder - War Thunder is a Free-to-play, WWII, Massively Multiplayer Online, Military-themed, Strategy, and Combat Simulation developed and published by Gaijin Entertainment.
AssaultCube - AssaultCube is a FREE multiplayer first-person shooter game. Taking place in realistic environments, with fast, arcade gameplay, it's addictive and fun!