Xonotic - Xonotic is a free (GPL), fast-paced first-person shooter that works on Windows, OS X and Linux.
BotBoxer - A first ever robotic punching bag with computer vision
Unreal Tournament - Unreal is a series of first-person shooter video games developed by Epic Games.
Timerly - A real interval timer
Quake - Quake is a series of first-person shooter video games released by id Software.
Liteboxer - An at-home boxing solution