This morning I found something called Protagonize.
It's a collaborative/interactive fiction community, found at http://protagonize.com/.

The idea is that you write a story "kicker", and others jump in with new branches and chapters.
I signed up as, unsurprisingly, joepub. At some point, I'm going to jump in with adding to new stories, and then start a couple of my own. Science Fiction looks fun. Mystery looks fun. Some day I might get adventurous and write erotica stuff.

Does anyone here have experience with that site? What's the community like?