Since early 2007 I, aka a-baby-rabbit, lurk here as a developer helping out when I have time.
Sauerbraten (Cube 2) is a simple but original 3D engine based on the novel idea of using an oct-tree entirely as the geometry, the game makes for a fast FPS with oldskool game play, including multiplayer, whilst providing in-game and cooperative editing.
Much of the 3D-UI (i.e. in worldspace) - the result being a simple but flexible gui with a range of the typical buttons, fields, lists, tables, tabs, etc
The Text editor as used in the UI
Much of the video and sound recording code
Some of the particle/explosion code
Enhanced the Mac OSX launcher with a fresh modern look - added map/demo/key preview, double-click to launch maps, etc
Lurked on forums and chat channels, occasionally being useful

Play testing