Here's another one: Talkyard — different from Discourse and Mozilla Talk, in that it looks more like Hacker News and Disqus: threaded comments, best first, Like votes.
It's free and open source, beta software (more risky than those two others), I'm developing it. There's SaaS hosting (no ads, no tracking — costs money instead) for people who don't want to install on their own server.
Demo: https://www.kajmagnus.blog/new-embedded-comments, read about it: https://www.talkyard.io/blog-comments
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Curious about how you have in mind that built-in commenting will look & work. Disqus, Talk and Discourse are all fairly different from each other, right, and I'm a bit wondering which approach you'll take. B.t.w. looks interesting with SSO & full community integration.
In the meantime, Discourse[1] and Talk[2] are great options that can be self-hosted if needed and integrate well. If you look at them you can see the level of effort that is required to do commenting, moderation, and spam protection well at scale.
[0] https://forum.ghost.org/t/memberships-subscriptions/377 [1] https://www.discourse.org [2] https://coralproject.net/talk/