Hacker News is actually pretty small in terms of how many people post. Other communities like it can be found in some small subreddits, discord servers, slack

Hacker News is actually pretty small in terms of how many people post. Other communities like it can be found in some small subreddits, discord servers, slack channels, irc, and some of the few online forums that didn't move to Reddit (like the Two Plus Two Poker forums). I think part of why HN stays good is they don't have a built in growth incentive (at least I don't think they do). You can imagine if you're running a site like Reddit you might really want to keep the site as high quality as possible, but for various real reasons you have stronger incentives to grow the user base, even at the expense of overall quality of community.