This website supports creation of self-organizing groups. Each group has a social media style “What’s new” where you can post short blurbs related to the group. In addition, each group can have a forum. Forums allow for creation of “topics” and discussion to occur via replies to that topic.
You can also look at the list of members, view their activity, and send them public (posted on the “activity” stream) or private (so only they can read) messages.