Comment systems

Cackle is a cloud services platform for increasing conversion using comments, feedback collection, online consultant and surveys.

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

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

Giscus is a comment system powered by GitHub Discussions.

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.

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

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

Twikoo is a simple, safe, free comment system.

Utterances is a lightweight comments widget built on GitHub issues.

Vuukle is an audience engagement and commenting platform.