Sacred Software
QnDMaze (Quick 'n' Dirty Maze) was written for a spontaneous 4 hour contest that happened in the #idevgames channel on irc.freenode.net. The game puts you in a 3-dimensional maze, navigating the twisting passages to find the exit and go on to the next level.
I'd already had the framework for a basic Cocoa OpenGL application sitting around, so this game had a bit of a head start. All I had to implement was the game logic itself. Automatic random maze generation turned out not to be as difficult as I would have thought. In four hours, I had a pretty solid little game.