Groups Plugin

Has anybody come across a plugin that will let a user be part of one or more groups and those in the group can see each other’s actions?

I don’t need full-on BuddyPress but something where a group of 4 friends could be created, labelled, and when content on the site is liked, commented on etc those actions can be viewed by all the group members. Group members are selected by email and if they’re not on the site they would be invited to join.

I can write it, but looking to shorten the development cycle.