Commento - A fast, bloat-free comments system to foster discussion on your website
Epoch by Postmatic - A native WordPress Disqus alternative with a focus on speed and privacy: 100% realtime native...
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.
Joint Comments - An embeddable comment widget for websites, blogs, ecommerce & static pages.
JustComments - Easy to set up, ad-free and reliable comment system