How to implement something like OG which the groups can manage on their own? I'm building a learning tracking site for a community where Mentors will match up with Mentees. I'd like them to create either an organic group or a paired relationship to share content (seen only by the two of them plus a supervisor, observer, or instructor). 

The catch is I'd like to let them do it on their own. In other words, I'd like to "get out of the way" and not maintain the actual groupings. 

Does this sound like a job more for Organic groups (OG) or User Relationships? Is there another technique that could get the job done more smoothly? 

And, how can they share content only amongst those with in that group or relationship? 

If I use OG, how can I best let users create and invite others without my intervention?
You could, for sure, use the Group module for this. Group allows for creating arbitrary collections of your content and users on your site, and grant access control permissions on those collections. It is available as of D7, and has a D8 version also. It is designed to be an alternative to Organic Groups. The Group module creates groups as entities, making them fully fieldable, extensible and exportable.

For more details about how Group compares to Organic Groups, refer to my answer to "What are the features of the Group module versus Organic Group module?". And for more details about the various roles and permissions, refer to my answer to "What are the various roles supported by the Group module?".

Resources


Community documentation for the Group module.
Video tutorial "How to use the Group module in Drupal 8 to manage editorial access control to different areas of a web site".