Planetpii is an e-mail-based RPG. Or, at least, that's what it was when this site was set up. It's become more of a platform for developing fictional (depending on your definition) races (Pinclans) and languages, and all that good stuff that goes with those.
Planetpii started as the RPG world of some Finnish children, one of whom—Natalia Laurila—is the founder of the mailing list and can take credit for causing the existance of much of what's out there now, including this site.