[AstralStorm]

Technically there always have been platforms that let you run a hosted forum maintained by others on someone else's host. These were typically paid.

But Discord has a different monetization nodel and that makes a world of difference. It's cheap.

It also has real time communication rather than delayed one, and has video and voice calls as well. On the other hand, it sucks even more than forums at maintaining a persistent knowledge base - but the actual solutions for that are wikis not forums.

The equivalent to Discord from old internet is IRC, not a forum.