3 Freeware available for Xonotic OSS FPS Free Full Game, see below
Xonotic is a free (GPL), fast-paced first-person shooter that works on Microsoft Windows, Mac OSX and Linux. Xonotic is a direct successor of the Nexuiz Project.
Xonotic places focus on community involvement as its principal driving force and structures itself to respect that. The aim of Xonotic is to become the best possible open-source FPS (first-person-shooter) of its kind.