Manufactoria

matthewdaly recently turned me on to Manufactoria, an online game in which you ostensibly build factories for testing robots. In reality you're programming a Turing machine in which state is determined by position on the factory floor.

I'm quite enjoying the game, but it wasn't until after I'd already solved the first 28 levels that I discovered, while looking at someone else's solution, that you could make conveyor belts cross.

Good lord. That certainly makes things easier!