I've looked and I don't think an extension exists for this, yet. Looking at a forum structure like QNAP NAS Community Forum - Index page
, it would be very helpful as a member to be able to choose which forums I wanted included in my board via a simple "subscribe" or "unsubscribe" at the forum (or category) level.
Dedicated administrators can in theory create this ability with open groups and appropriate group forum permissions, but I think it would be useful functionality to offer in via settings in the User Control Panel.
Normal people… believe that if it ain’t broke, don’t fix it. Engineers believe that if it ain’t broke, it doesn’t have enough features yet. – Scott Adams