utterances

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

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.

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

Disqus is a comprehensive, worldwide blog comment hosting service for websites and online communities that leverages a networked platform. This popular service allows website owners to easily integrate a robust commenting system into their sites without the need for complex backend development. Disqus offers features such as real-time commenting, social media integration, spam filtering, and moderation tools. It also provides a single sign-on capability, allowing users to comment across multiple websites using their Disqus account. The platform's networked nature enables cross-site discussions and helps build engaged communities around content. Additionally, Disqus offers analytics tools for website owners to track engagement and understand their audience better.

Twikoo is a simple, safe, free comment system.