A 3d rendering and game engine library written in C++. It is expansive - collision detection, software rendering, various file load/parse libraries, and on and on.
I spent a lot of time coding this many years ago while still in high school. Much more recently, I captured a video of the demo running live - it's available at http://vimeo.com/35163009.
The project compiles and runs in Win XP in the Watcom 11 IDE. It does not work from the (much newer) open source Watcom IDE, so you will have to hunt around to find the original version 11 software.