Large web forums and content management systems might do more keen things, but I predict they'll seem like overkill for your purposes. It sounds like you want to do something wikiish, but you need to add some kind of ACL system. The Kwiki wiki system is very extensible, and while writing an access control plugin wouldn't be trivial, it would be possible.

Take some time to write a little story that answers the question "How will people use this?" Once you've written down a good use case or two you'll be able to see whether it looks like a wiki or like something else.