Sure. Just look at Wordpress… it’s a blogging platform rather than a forum, but it has an ActivityPub plugin available that allows federation of blog posts and comments. ActivityPub is a standard published by the W3C (the same organization that oversees the HTML standard, among many others). Anyone can implement the standard in their software if they want to.
Because they’re alternatives to Twitter?
Not everybody on the Internet cares about censorship, data leaks, or centralized services. In fact, most people don’t. You just happen to be in a bubble of mostly like-minded people here on the Fediverse. For everyone else out there, now that their digital house is on fire they just want to find a new house that’s as close to their old one as possible.