The tandem story is often used in creative exercises to force people to work as a team. When the story is turned over to you do you keep it going down its desired path or do you add an unexpected twist? Or do you completely disregard what was written and do your own thing?
Fictive is simple: Start a story. Set a max word limit. Invite your friend(s) and start writing.
Additional Info: The concept for Fictive is loosely based on the exquisite corpse drawing technique. Instead of users working together to draw a picture, users work together to build a story.