Great news for everybody that loves to read and write fictional litterature!
I’ve found a really good site for collaborative storytelling: CoST.LI – where writing stories together is great fun! The site is very new, and improving with new features almost daily. Currently it features a nice ranking system, quite similar to the reputation mechanism of sites like StackOverflow and its sister sites in the stack exchange community. There is also a nice toplist where you can compare yourself to others.
Best of all, it’s totally free (some google ads are meant to support it, good luck on that one!), and it uses OpenID for authentication.
Give it a try! Its multilingual, currently with free stories in English and there are some impressive ones in Swedish too.
So, what is Collaborative storytelling? Simply put: someone writes a story, and another one can continue on it. One of the most interesting features on this site is that each chapter can have several continuations, so there can be potentially an unlimited number of stories in the end.