DISQUS - Disqus is a global comment system that improves discussion on websites and connects conversations across the web.
Juvia - A commenting server similar to Disqus and IntenseDebate
Hyvor - Hyvor is a privacy-focused and fully-featured commenting system created for almost all kinds of web applications and blogs.
Joint Comments - An embeddable comment widget for websites, blogs, ecommerce & static pages.
Realtidbits - Powering the Realtime Social Layer for Entertainment, Local Media and High Traffic Blogs.
Hyvor Talk - The Best Commenting Platform For Your Website