CreaStoria is a game where players become authors, creating growing trees of collaborative flash-fiction. Each node in the tree is a short (under 120 characters) story written by a single author. Authors can write more than one story, but cannot continue their own story (in otherwords, during play, a random node is chosen for them to continue, but it can't be one that they have contributed). Roll over the nodes to read stories, and give a thumbs up (or down) to stories you like (or don't).
The game is available in both English and Italian, and you can play here. The tree is made using a force-directed layout in d3js - although the nature of the data doesn't strictly need this kind of layout, the bouncing is pretty. The tree updates dynamically, so you can watch your stories "pop in" as you play. You can also view the Italian story tree.
Read a bit more about the game here.