A dungeon crawler game with no artwork, sound effects or music, but lots of ray-casting, lighting, visibility and collision detection.
In other words, programmer heaven combined with programmer art!
There are 13 levels in total, and some of them are fiendishly difficult. Each level also adds to the story line.
Note that you need to have Microsoft Silverlight 4 or newer installed. This game works on Windows and Mac OS X. It does not work on Linux (the port of Silverlight to Linux, called Moonlight, only supports Silverlight 2).