DISQUS - Disqus is a global comment system that improves discussion on websites and connects conversations across the web.
Joint Comments - An embeddable comment widget for websites, blogs, ecommerce & static pages.
Hyvor Talk - The Best Commenting Platform For Your Website
Hyvor - Hyvor is a privacy-focused and fully-featured commenting system created for almost all kinds of web applications and blogs.
Schnack - Schnack is an open source commenting system written in JavaScript.
Commento - A fast, bloat-free comments system to foster discussion on your website