If a site has a 'niche' theme and you want to find people with likeminded interests out in the Fediverse, the searching would be useful.
Correct me if I am wrong, but Mastodon doesn't seem to have categories, Ive only seen it on Lemmy.
In a way a category on Lemmy is like a nodebb instance, as most nodebb instances are for a certain area.
So one might argue that posting on a particular nodebb forum is akin to posting on a Lemmy category?

@eeeee a forum is usually structured around a common theme, yes. For example, community.nodebb.org is centred around support/discussion for NodeBB.

However, nothing stops someone from creating a general-interest forum, and that's why I prefer to think of NodeBB categories as like Lemmy communities.

You are correct in that Mastodon does not have the concept of categories. In fact that have not much concept of organization of content outside of reply-trees, and that is partly by design and partly by the constraints from the microblogging style.

@eeeee @julian There are topic-specific Lemmy-based websites. startrek.website, ttrpg.network, etc. exist, and function much more like a traditional forum than a catch-all "general purpose" social networking or social media aggregation site, like Facebook or Reddit.

And I personally have argued, and continue to argue, that the Reddit model doesn't really work on the Fediverse. That the desire to create a simulacrum of large scale, centralized social media doesn't really scale well once you have multiple websites, and that focusing on a local-first framework is the more logical and more sustainable model long term.

I don't think modeling Lemmy communities as being the equivalent of an entire nodeBB website will stand the test of time. The idea that the hosting website matters continues to seep into the thinking of many Lemmy users, and so it should matter to non-Lemmy websites, too.

People on Lemmy sometimes ask if there's a way to view communities by hosting site. This is a view that the Reddit-like UI has no natural way of supporting, but forums do. I would love to be able to see remote groups listed as categories in sub-forums ('sections' seems to be the nodeBB jargon?)

I've brought up elsewhere, too, about being able to create my own categories-style layout in /world; assigning remote groups to my own pseudo-sections would be amazing. Having the option to have these personalized pseudo-sections show up in the main categories view would be even better.

I've also mentioned in the past having a way for regular forum users to 'boost' posts from /world into official forum categories. There are a couple of ways to imagine this, with the most straightforward being just moving/copying the topic into the category, just as admins can currently do. But there's also the cross-post feature from Reddit/Lemmy, where there's a back-link to the original post, and the content displayed in a block quote. I see value in both of those options, though I can't imagine any given forum would want to support both.

User pseudo-categories could even be shareable. There's no reason they need to be strictly private (though, of course, users should be able to choose to make them so, if they were shareable). They'd functionally be like lists on Twitter, or custom feeds on Reddit, but with a section/category UI. Or not, I guess -- they could be treated as feeds, too, but I'm kinda sorta very, very over "feeds", personally.