DISQUS - Disqus is a global comment system that improves discussion on websites and connects conversations across the web.
Commentics - Commentics is an advanced PHP comment script with many features.
Joint Comments - An embeddable comment widget for websites, blogs, ecommerce & static pages.
RbComment - RbComment - Zend Framework 2 module for drop-in, self-hosted comments, with email notifications...
Hyvor - Hyvor is a privacy-focused and fully-featured commenting system created for almost all kinds of web applications and blogs.
talkatv - talkatv is an open source comment service much like ...