Sauerbraten, which is also commonly referred to as "Cube 2", began as a redesign of the original Cube game and since 2004 they have been making quite a bit of progress in improving the game-play as well as the graphics. The graphics engine is supposed to be much-improved with Sauerbraten release due out in 2011, we are told, but the 2010 "Justice Edition" release does carry some interesting changes and does offer some graphical enhancements.
Sauerbraten 2010-07-19 introduces new player models along with many new multi-player maps, multiple new game modes, a mini-map has been added to the radar system, an optional Quake-like mouse acceleration mode, rotational friction for rag-dolls, a motion blur effect, and many other in-game changes and fixes. The new game modes include efficiency CTF, efficiency protect, hold, insta-hold, and efficiency-hold.
When it comes to the graphics capabilities of Sauerbraten 2010, new changes in this area include support for alpha-blended textures, color scaling for diffuse textures in all shaders, support for fogging and coloring sky-boxes, multi-threading of the calclight command for lighting threads, a GLSL render path, support for uniform buffer objects to GLSL skeletal animation path, improved skeletal animation blending quality in the fixed-function mode, and improved adaptive sampling for calclight.
The complete list of changes for Sauerbraten 2010-07-19 can be found on the history page. The latest Linux, Windows, and Mac OS X versions of Sauerbraten can be downloaded at Sauerbraten.org.