An online community should feel like an online pub. It should have a vibe, some regulars, inside jokes, and a decorum that is somewhat well enforced. They're cosy places where a sense of belonging encourages participation and good behaviour. HN is like that. Small subreddits are like that. Group chats are like that. But now every social media website became like that one pedestrian street with the H&M and the McDonal…
I would maybe add early Facebook for the social, but not funniest part.
Some discord servers do a good job at recreating the vacuum of IRC (albeit every single one of them has always way too many channels) but the vacuum of forums is just not well replaced.