Itching to run Cortex Plus / Prime
West Marches is the name of a famous internet campaign, where lots of PCs were allowed to pop in and out of the story, basically playing with whatever party members showed up. I'm planning on doing something similar here, where the PCs are a loosly affiliated group, set in an open world where they can go places and advance the story however they please. So the PCs can split up, go different places, explore, whatever. This somewhat mitigates some of the problems of PbP, in that if someone doesn't post, their PC just wanders off after that Scene (and the GM may do with them what they wish, MUWAHAHAHA), and the larger narrative continues with the PCs that are still participating, and folding in any new characters as we go.
Exalted is something of a kitchen-sink setting. Largely anime-inspired fantasy, but with elements from a great many genres represented, and many campaign styles possible. The part I like most is that the setting more or less allows PCs to do whatever they can imagine, and the system allows the same, so there's plenty of room for custom builds and I shouldn't have to say, "no" all too often.
I'm considering opening the game up without a setting in mind, and the first group of players that show up can decide where they'd like to play.