The Procedurally-Generated Dog Simulator is a fun illustration of pathfinding and cellular automata. All you do is walk around a cave, being followed by a single-pixel pup who is liable to get distracted by treats or scared off by skateboarders.
Via Boing Boing.
See also:
* Mudeford, a free dog-walking simulator in glorious full 3D.
* Dog names generated by a neural network.