Portrayl , according ot their website “is a place where writers showcase their work. You can start a story and add a chapter at a time. When you decide you’re finished, you can create a pdf ebook and also rss feeds of your story. Here’s the cool part – other people can add chapters to your story – but your chapters stay intact. When someone adds to your story it branches off into a new direction.
Ficlets: according to their site “a ficlet is a short story that enables you to collaborate with the world. Once you’ve written and shared your ficlet, any other user can pick up the narrative thread by adding a prequel or sequel. In this manner, you may know where the story begins, but you’ll never guess where (or even if!) it ends.”