Kriegspiel is a chess variant where you don't get to see your opponent's moves. Instead you just get to move his pieces around to where you think they are. It normally requires 3 people and 3 boards. One person has to be the referee and it's a hard job since he has to watch for check and inform people when their pieces get taken. It's an ideal job for the computer. If you ever play it, go for the fool's mate, it always works the first time.