The latest change to the ActivityPub integration for NodeBB introduces the concept of "group actors" to categories.
This change means that categories can be configured to be visible to other applications connected to the social web (including Mastodon, Misskey, and also other NodeBBs!)
When followed, it means that any post made to the category will be automatically shared to anyone who follows that category.
NodeBB already supported this locally. You could set your watch state for a particular category to "tracking" or "watching", the latter allowing you to be notified of new posts.
Also of note is that remote replies to topics contained within a category will also be shared to the category's followers. This distinction means that you can effectively follow a specific category or sub-category in order to stay up-to-date on all discussions within that category.
As of today, users cannot create topics in a category from the social web (e.g. I cannot create a new topic in a NodeBB category), yet. That will come soon.
For the NodeBB community forum, the following categories are followable for now:
