Also works with !communityname@whatever.tld for communities.

In general that's a good idea because you should never trust content coming from somewhere else (even in an S2S context) For reference, NodeBB literally sanitizes the bejeezus out of what it gets from anywhere. All classes are removed, all attributes are removed. I want it as close to semantic HTML as possible, and classes/attributes mean absolutely nothing because: I don't use the same CSS classes Attributes may not follow my own rules for when and where they are added. For example, Mastodon messes with any URL it federates out. It chops the anchor text in half, hides the rest behind invisible or something, and adds an ellipsis. invisible does something different in NodeBB, so there is a CSS conflict here. I strip everything and just show the URL as it was intended.

It took a few days for instances to be upgraded and admins to fill in their profiles but it's looking much healthier now! https://piefed.social/auth/instance_chooser

Discourse's Trust Levels are an interesting idea, but not one that is novel. It was lifted almost entirely from Stack Overflow. At the time, Discourse and Stack Overflow had a common founder, Jeff Atwood. There's a reason Stack Overflow is rapidly fading into obscurity... its moderation team (built off of trust levels) destroyed the very foundation of what made Stack Overflow good. I am also not saying that what we have now (first-mover moderation or top-down moderation granting) is better... merely that should you look into this, tread lightly.

On piefed.social I don't want to have much NSFW content to oversee because it's an extra moderation burden but there is plenty of it on other instances. If you go to https://piefed.social/auth/instance_chooser and then filter by ’NSFW content available’ you’ll see the instances that allow NSFW communities. Of those feddit.online has been around the longest and will have the deepest back catalogue but most of them will be fine for casual browsing. Before you make an account on a new instance, go to the_instance.tld/communities then into the advanced search and switch on NSFW to check how many NSFW communities have been federated to that instance.

I notice nobody responded to you... yes notifications work fine on PWAs. No additional apps required. NodeBB has supported them for a couple years, and Piefed can do so with some effort too. rimu@piefed.social happy to discuss how we did it — all standard web tools! I am not 100% sure there is iOS support, though. Supposedly there is, but we got some reports saying otherwise.

Within a chatroom would be a first step, but I've noticed that the best is indeed to have a subchannel structure. And yes, Zulip is the best one for long topic-based conversation, that's why Piefed uses it, as stated in the OP :D