Forums are not dead
I’ve recently started to take counter-measures so I can be empowered to work on what I need when I need, instead of being constantly interrupted by notifications. Forums and email can be a good solution to get asynchronous conversations you can get back to when you have time for it.
I have (yet another) blog post about it in the writing, but for now I have found that the forums ecosystem has evolved since the good old phpBB days of my youth. There is still a lot of interest in that area!
Discourse the almighty
I don’t think anyone is going to discover Discourse here, but of course it’s worth mentioning. It has become the ubiquitous forum software. It’s open source, and the company behind it has a paid hosting offering that can become pricey as your moderation team grows.
I find the “home” interface to be a bit confusing. Overall Discourse uses a lot of white space to delimit things. The category and thread views are better organized and easier to read.

Two useful built-in features to me are the mailing list mode and the RSS feeds generated for each category or thread.
Flarum
As with every popular software, some people accuse Discourse of being bloated and slow, though I have never faced those issues myself.
Flarum looks very similar to Discourse, but advertises itself as fast(er). It is also free software. I like that it feels much more lightweight and decluttered. The UI is simple and to the point.

Flarum doesn’t natively support mailing list mode, which is a significant downside for me since I don’t intend to visit forums “just because.” I’d rather be notified that there is a new message in a section I care about and reply directly by email.
It supports extensions. I tend to be particularly wary of extensions and will favor core features over third party plugins whenever possible. Third party plugins are a last resort to me, because I don’t know how sustainable they are, whether the people behind them will be motivated to keep up with the platform’s evolutions, etc. Those feel very brittle.
NodeBB
I only learned about NodeBB today, although the project is not recent (their demo instance has messages from 2022). It’s open source and self-hostable.
Their own instance looks quite overhwelming to me with that many pinned messages. I struggle to make sense of it and would rather have a simple list of categories, from which I could browse topics.

The interface is also quite had to read for me on mobile, with its floating element, inconsistent text size, and information all over the place. This should be “easily” fixable with a custom theme, that they do seem to support.

One of their developers told me they were working on ActivityPub integration, and I’m not entirely sure how I feel about it. I don’t know if there is a strong use case for it, and I’m not sure what problem this would solve.
Topicbox
Topicbox is slightly different, in the sense that it’s email-first with a frontend to make it more accessible. I personally love it but deeply regret that it’s proprietary.

I’m sure there are other options I’m not aware of yet, but those were the main ones I’ve bumped into!