Invision Community - Invision Community is a flexible, integrated set of apps for building communities on the web.
DISQUS - Disqus is a global comment system that improves discussion on websites and connects conversations across the web.
XenForo - Intuitive. Social. Engaging. Fast. XenForo brings a fresh outlook to forum software.
Commento - A fast, bloat-free comments system to foster discussion on your website
Discourse - Discourse is an open source discussion platform built for the next decade of the Internet.
Commentbox - Commentbox is a jsf component that allows quick realization of a comment functionality