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Juvia - A commenting server similar to Disqus and IntenseDebate
Commento - A fast, bloat-free comments system to foster discussion on your website
DISQUS - Disqus is a global comment system that improves discussion on websites and connects conversations across the web.
coComment - coComment is a service for managing, powering and researching conversations online.
Commentics - Commentics is an advanced PHP comment script with many features.