A new site for collaborative writing was started recently. Ficlets lets authors write short fiction snippets. The stories grow by others writing sequels and prequels to the existing stories.
Looks like a real fun way to share and build stories.
"The Church holds that life is a game played by an agency even above the gods, referred to only as the Gamers. Gamers are incarnated in the real world by select and colorful individuals. Those heroic individuals are the focus of the game, while everyone else is merely a backdrop for their exploits" From "Believe it or Else"