Ask HN: What makes a good online community?

I'm interested in what makes a good online community. Is it the community software with rules and reputation and gamification? Is it the moderators that help enforce the rules? Is it something else? I'm especially interested in examples, why you think they're good, and how long you've been involved.

  • Well, we are on HN: it is a good community because of both quality technical content and a engaged userbase.