[Request]Closed groups of users

I have a simple idea for which I didn't find any extension so far.

Give the ability to users to create groups of discussion where they can share documents/photos/ and discuss/chat in closed groups.

For instance, student groups could be made where they can share documents over a project and discuss it in a closed space/room. This could give a working environnement for small groups inside larger communities.

I think that would be great. I don't have any idea on how to program that, but if it could exist some day, it would be terrific.