Alright. *cracks knuckles* Let's see. The Wayback Machine isn't being very friendly toward me right now, but between that and my own memory, I've only been able to come up with four. There's no way this can be right. Let me know if you remember anything I missed.
THE (IN)COMPLETE IDIOT'S GUIDE TO THE PONYVERSE.
2031 was my first foray into the world of RP, and it's the one that I actually finished. It was really, really bad, because I was literally twelve years old and the community hadn't attracted very many (read: any) decent RPers yet, but it made it all the way and for that I'll always be proud of it. It was a pretty generic, uninspired post-apocalyptic adventure with a fantasy kitchen sink thrown in for the hell of it.
The Fall of Humanity was the ill-conceived prequel to "2031," which fell apart after a core member of the group (geriand) got banned from the forums for... What did geriand get banned for, anyway?
For Those Who Have Heart was my Kingdom Hearts RP. I liked this one so much, I tried to start it up twice. We made it a world or two in each time, this one probably just fell apart because Pony Got Bored™.
Venthus: Age of Exploration (or some title to that effect) was my baby. I'd posted a (not very good) fantasy series I'd been writing with a girl from school on the Off-Topic boards, and that got enough attention that I set an RP in the universe. The OP was two posts long and full of obscene amounts of worldbuilding, which was pretty unprecedented for a URealms RP at the time. I got character sheets that exceeded a post in length, too, which was really cool. Shadowbolt654's in particular comes to mind. Chocobo nominated me for one of those forumer achievement awards for that OP, and I think Tirin's character sheet got him an award, too.
This one fell apart when Chocobo wrote a character-introduction post that just had his character staring at ceiling fan, contemplating the nature of the universe, and I had no fucking clue how to respond to it. His storyline came to a halt as a result, and eventually dragged the rest of the game down with it.