DISQUS - Disqus is a global comment system that improves discussion on websites and connects conversations across the web.
Commentbox - Commentbox is a jsf component that allows quick realization of a comment functionality
IntenseDebate - IntenseDebate's comment system enhances and encourages conversation on your blog or website.
SmartComment - SmartComment is a web-based software for public comments and outreach campaigns.
Commento - A fast, bloat-free comments system to foster discussion on your website
Vuukle - Vuukle is a multi-point user engagement platform.