Sumotori Dreams is more of an exercise in creating self-balancing characters than it is an actual game, but the utter hilarity involved makes this little gem worth keeping. While it offers little to no gameplay value it delivers something no other game can: a physics simulation of two incredibly drunk people shoving each other and trying to stand up after falling over countless times. It is free software.
This home-brewed sumo-wrestling simulation uses a tiny installer and advanced artificial intelligence to create a simple yet enjoyable competition. Knock over your opponent or knock him out of the ring to win a point. The first to five while leading by 2 points wins the game.