A really fun application of Wiki is to allow a group of people or students, to collaboratively write a web-based, non-linear story. By web-based non-linear story, I mean a story where at each page, the reader chooses the hero's actions from a list of links. For example, see these stories (sorry, they are all in French):

    http://lizzy.iit.nrc.ca/CyberClub/public/wiki.cgi?Jeux_d_Aventure

These stories were all created by teams of Grade 4 students (2-3 students per team) over the course of 5 1-hour sessions.

The stories were created using the YetAnotherWikiClone system.

-- AlainDesilets 

I wish there was an English translation.

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Not wiki based, but a similar thing is done with the "Story Engine" http://www.qwantz.com/storyengine/index.asp