DISQUS - Disqus is a global comment system that improves discussion on websites and connects conversations across the web.
HashOver - HashOver is a PHP comment system intended as a replacement for services like Disqus.
Commentics - Commentics is an advanced PHP comment script with many features.
talkatv - talkatv is an open source comment service much like ...
Commento - A fast, bloat-free comments system to foster discussion on your website
UpContent - UpContent is a content discovery tool that helps businesses to drive meaningful conversations with their audiences.