Remember the choose-your-own-adventure books? At each page you can choose from 2 or 3 decisions which take you to different pages to continue the story. They are sort of the minimalist version of adventure games.
Here's a neat web 2.0 site that let's people create these things online collaboratively.
Protagonize.com is an online writers' community dedicated to the (nearly) lost art of the adventure, a type of collaborative fiction. Once an author writes a story, others can post branches to that story in different directions.