Organic Groups module for drupal, enable users to create and manage their own ‘groups’. Each group can have subscribers, and maintains a group home page where subscribers communicate amongst themselves.
A website of a federal client, that I worked on, had custom groups functionality, implemented using taxonomy. It became out-of-scale to manage that way, any longer and also they with restricted, by that. This module, crawls through each taxonomy term, create an organic group, based on those terms. Also migrate all users, posts, likes, comments, interaction history, … from being assigned to taxonomy term to being part of organic groups.
Technology : Drupal