There are a ton of free comment widgets available- Facebook comments, Disqus, Livefyre and many more. They're outnumbered by blog posts on replacing these bloated, privacy destroyers with a custom systems that use GitHub issues as a backing data store.
Enter https://utteranc.es, my take on hosting blog comments on GitHub issues. Lightweight, easy to configure and secure. No need to worry about GitHub API rate limits, managing server-side code, manually linking blog posts to issues or forcing users to leave your site to post a comment.
I had a lot of fun building this app, it served as the POC for the GitHub issue integration in Microsoft Docs. Much of the GitHub API and OAuth related code is shared. There are some features that haven't made it into docs yet like markdown preview. On the other hand, we've implemented reactions in docs, which hasn't been backported to utterances yet. As of this writing, users have opened more than 2,250 issues via the GitHub based feedback system in Microsoft Docs. Pretty crazy. Kudos to the content teams that are keeping up with all the issues!
If you have any feedback let me know in the comments below or open an issue/PR.