DISQUS - Disqus is a global comment system that improves discussion on websites and connects conversations across the web.
IntenseDebate - IntenseDebate's comment system enhances and encourages conversation on your blog or website.
Geist.chat - Add feature-rich responsive comment sections to your website.
Discourse - Discourse is an open source discussion platform built for the next decade of the Internet.
Viafoura - Viafoura is an easy-to-integrate social monetization platform that enables your to better engage, understand and monetize your community.
GraphComment - Add modern discussion and social interactions to your website