I wonder, what are some that folks have come across. That are amusing that is, and not FATAL. I know Dune's run some Maid system. Here's something vaguely amusing that someone linked a bit ago, trying to get Touhou into D&D. Wacky that.
http://gensod20.host-ed.net/index.html
Oddest one that I have is Creeks and Crawdads. You play semi-intelligent crawdads, the most advanced species remaining after WWIII. The examples of play are hilarious.
Seconding the various attempts to force Touhou into D&D, be it 3rd or 4th edition.
Link Maid System Dunefar :)
Dogs in the Vineyard: you play itinerant Mormon preachers casting demons out of people. Actually quite fun with the right group.
Truth and Justice: A superhero game without hitpoints; instead, damage is applied to your skills and powers. So a punch can quite literally cause you to lose some of your Outdoorsman skill, Criminal attribute, or Darkvision power.
Anger of Angels: basically a port of In Nomine to D&D3.5
Dawn of Worlds: a collaborative dice-driven game the end result of which is a newly-created campaign setting for a fantasy RPG
Fireborn: reincarnated dragons engage in magic-fueled martial arts in modern London while undergoing flashbacks to their former lives