A while ago I discovered Minecraft4k, a java demo written by Notch fitting into a 4kb object file.  He used software raycasting to rasterize a large 3d array of voxels. The original demo can be played here as an applet:

https://mojang.com/notch/j4k/minecraft4k/

At the same time I found that Notch had made a Javascript port of the same basic engine, minus user input.

http://jsdo.it/notch/dB1E

One awesome thing about these two demos is that all of the textures are synthesized proceduraly for space saving reasons.

Seeing his work, I got a strong urge to port the code to C++ and SDL.

Grab the source code here:

http://pastebin.com/jfjqAas8