Marble Computing

Marble Computing is a game about logic and computing, with an extreme restriction of using marbles.
It is availible to buy on Steam.

The games source code can be peeked at here: /git/?p=fishladder.git
And the engine code (codenamed Voyager): /git/?p=vg.git

The game and the engine's source code are written entirely in pure C, for simplicities sake.