Comment systems

Vuukle

Vuukle is an audience engagement and commenting platform.

Giscus

Giscus is a comment system powered by GitHub Discussions.

Disqus

Disqus is a worldwide blog comment hosting service for web sites and online communities that use a networked platform.

Livefyre

Livefyre is a platform that integrates with the social web to boost social interaction.

IntenseDebate

IntenseDebate is a blog commenting system that supports Typepad, Blogger and Wordpress blogs. The system allows blog owners to track and moderate comments from one place with features like threading, comment analytics, user reputation, and comment aggregation.

Isso is a lightweight commenting server written in Python and JavaScript, referred to as "Ich schrei sonst" in German.

Twikoo

Twikoo is a simple, safe, free comment system.

utterances

Utterances is a lightweight comments widget built on GitHub issues.

Commento

Commento is a tool for fostering discussion and improving engagement on websites.

Question2Answer

Question2Answer (Q2A) is a popular open-source Q&A platform for PHP/MySQL.