I used to use phpBB back in the day and switched to Xenforo when their development pace slowed to a crawl and Xenforo's been a huge improvement in almost every way but one: In phpBB, there's a user-facing groups management page where users can add themselves to user groups (e.g. allowing people an option to join a politics group to see a hidden political discussion forum). I wish Xenforo had that. Is that what you mean?