Ask HN: Great examples of site/app engagement for better discussion?

Ask HN: what are great examples of engagement metrics / fitness functions on a site/app which encourage a better quality community/content?

The common narrative is that sites like Facebook and Twitter aim for engagement metrics which generate outrage. Instagram seems to generate overly cosmetic / vapid content. Stack Overflow and Quora encourage rule following and voluntary knowledge exchange.

Reddit/Imgur generally encourage karma farming, but have lots of diverse incentives within communities.

I’m experimenting with a set of incentives for a site which can pay (in either points or perhaps crypto tokens) for quality questions and answers, but punish for low effort, low quality, spammy content. I’m also considering invite-based reputation sharing (like Russian hacking/malware/carder forums which require a vouch by a reputable member before a new member can join, thus tying the reputation of the voucher to the vouched).

I’m also considering being able to revoke or suspend reputation / payouts and making it contagious to the user’s closest members.

Are there any examples of community incentives which have encouraged an abnormally strong community that didn’t pre-exist?