Wikis work great for collaboration because of the history function for each page that allows everyone to see previous versions.

I use it extensively for my game. Everything is passworded to prevent drive by people from editing but all the players can make additions or changes.

It also sounds like you could use Google Wave that is what it was originally meant for. It has been mostly shut down now but you might still find someone using the API for it. Or just Google Docs and share them with a specific group.

BOB