I'm not sure if this is actually classified as a game but here it goes...
So I will start with one sentence and you build on it
Ex. Post #1 Once upon a time there was a great black horse
Post #2 His name was sir.Alexander
Post #3 He lived in a enchanted forest in spring field. Etc. etc.
So I'll start
There once lived a great horse in the desert plains, the few people who have seen her call her mystic.