How to a kind of intranet or ...

HI,

For a non profit org (church) I want to create a kind of intranet.
The purpose is to create an environment to create groups to share messages and questions. Where everybody from this group can see messages and interact.
I thought about the Forum or Community plugins for this purpose, but don't know if they are the best solution.

They will have a group for ex. Group 1, Group 2, Group 3. Each member can access only messages from own group. i.e. member from group 1 sees only messages from group 1 and so on...

Suggestions????

Thanks!