While there are many open-source games available (just see the recent discussion about the most advanced GPL-ed FPS), most of them are based upon the ioquake3 game engine that in turn is based upon id Software's open-source id Tech 3 engine. There's also games like Nexuiz that use the DarkPlaces engine and then also Warsow that uses QFusion. There have also been projects like XreaL that seek to greatly expand upon the visual capabilities of the ioquake3 engine, but many of these projects go on without ever making it to a release stage. Today there is yet another open-source game engine in development.
We were contacted last night about the developer of this new game engine (called the "AnKi Engine") that's supported on Linux; in fact, we're told that's where it's been solely developed on Linux and that it should work on Windows but has never even been built there yet. AnKi offers deferred shading, shadow mapping, Screen Space Ambient Occlusion (SSAO), High Dynamic Range (HDR), Spherical Environment Mapping, Light Scattering, Parallax Mapping, and other OpenGL advanced features. The GPLv3 engine uses SDL, GLEW, OpenGL, and libjpeg. Not only is the engine GPLv3, but the visual assets are likely to be put under the Creative Commons, which will please many users.
Unfortunately there is no playable demo or anything at this stage, but there is a short video that showcases the AnKi engine (embedded below). We were contacted by "Panos", the developer of this engine, as he actually looking to launch a benchmark / tech demo of AnKi for the Phoronix Test Suite. Panos mentions the engine should be ready and complete enough for at least such a demo. He is currently looking for ideas for this demo, so if you have any, please share them via the "comments & discussion" link below.
The AnKi video looks fairly nice, but we will reserve final judgment until the demo/benchmark is actually released. We also need to hope this project does not fade away prematurely like many of the other free software projects around.