And I'm not even talking about #Discourse which, by the way, will NOT let #Mastodon users interact with forums the same way as registered forum users. No, really not. Discourse will only advertise new threads through #ActivityPub. It will NOT let users of Mastodon etc. reply to threads. It will NOT let users of Mastodon etc. start new threads.
I'm talking about projects like #Friendica (est. 2010, 6 years older than Mastodon, 8 years older than ActivityPub) and #Hubzilla (est. 2012, 4 years older than Mastodon, 6 years older than ActivityPub). They had forums implemented long before there was Mastodon and long before there was ActivityPub.
Just like Discourse, these forums can be fully moderated. But just like #Guppe, just about everyone on every Fediverse project can interact with them. And unlike both Discourse and Guppe, they can be public as well as private/members-only.
dekkzz76