Xonotic
Superproject containing build scripts and tools to download assets
...Players can enjoy a wide variety of multiplayer game modes—from traditional deathmatch and team captures to experimental variations like Nexball and Freeze Tag—each designed to exploit high mobility and deep map knowledge. The game includes dozens of official and community-created maps, robust server browsing, customizable HUD and controls, and even an integrated statistics system called XonStat for tracking performance.