BoomWriter

http://www.boomwriter.com/Schools
Creative writing using technology.

Students use the preexisting story starters to write their own stories collaboratively.  Other students then vote on their favorite stories.
Encourages students to read and write.  Once students write the next chapter to their story starter it is then submitted to the teacher who can either approve the story or request revisions.  Once all the entries are approved the teacher initiates the voting process.  Students read their peers work and cast votes for the chapter they like best.  It is completely anonymous and the students do not know who wrote what piece.  Great way to encourage more writing in the classroom

And its completely free.