Merindian Rummy
I'm not quite sure why this 15-card, multiple deck variant on 500 Rummy took on a life of its own, but it is strangely addictive. I came up with most of the rules on the spur of the moment during a roleplaying game one day (Merindia was a country in the world where that game was set), and then tweaked a little bit for playability. I taught it to a bunch of folks, and they taught it to a bunch of others, and pretty quickly it lost its gaming connection, which meant the name made no sense to new players, I suppose.
A few years ago at a convention in Atlanta, a friend saw a group of people playing what was clearly Merindian Rummy...but they called it Indian Rummy, and had heard a story about how it was created by someone in India. She explained the actual name and that she knew the creator personally, but apparently they didn't believe her...and I have to admit their story was a lot more plausible than the real one. I'll try to get around to posting the rules in the near future.