It took me a while to wrap my head around Discourse’s organization and
how to coerce it into something that I could use to teach classes.
Discourse calls groups of topics (top level posts) “categories”.
“groups” are groups of people. Groups can be used to limit permissions
on categories.
Each category can have many topics. No problem.
The permissions system handles this. You can also create categories
where some people can only view (they can reply, but it has to become
a new topic in adifferent category), or only view and reply to topics
in the category.
You’d need to find a creative solution here. Topics exist in only one
category. You can move things between categories. You can also use
tags as an organizer. Users can watch tags. People can invite people
to join or notice a discussion with @username.