Tesseract

Tesseract is a first-person shooter game focused on instagib deathmatch and capture-the-flag gameplay as well as cooperative in-game map editing.
Tesseract provides a unique open-source engine derived from Cube 2: Sauerbraten technology but with upgraded modern rendering techniques.

The new rendering features include fully dynamic omnidirectional shadows, global illumination, HDR lighting, deferred shading, morphological/temporal/multisample anti-aliasing, and much more.