collaboration wordpress plugin

i am looking for a add on to my website website is WORDPRESS here is what i need i want to give out user names and password to people that i want to participate the person with the user name and password would be able to log and can do few things the user would then be allowed to do 1: write a story and submit it fore everybody to see the user can edit the story or add on to it more any time he or she wants. the user will be allowed to vote on the best story submitted the user only gets one vote cant vote for there owen story. stage 2: Characters. user would be able to submit characters for the winning story. other users whit log in would be able to comment on other peoples story and characters