Some of these came up a while back over on What’s with “Discuss on Mastodon”? Here’s the list I compiled there:
- HTML Comment Box (relies on Google forms)
- Utterances (relies on GitHub)
- Cusdis
- Netlify
- Komments.cloud
- Commentario
- Isso
- Chirpy
- Remark42
For the time being though, I’ve just been crossposting things to Dreamwidth, which has a comment feature built in.