DISQUS - Disqus is a global comment system that improves discussion on websites and connects conversations across the web.
Freshservice - Freshservice: the one-stop cloud solution for all your IT management needs.
Reddit - Reddit gives you the best of the internet in one place. Get a constantly updating feed of breaking news, fun stories, pics, memes, and videos just for you.
Freshdesk - Freshdesk is a cloud-based customer support software that lets you support customers through traditional channels like phone and email, social channels like Facebook and Twitter, and your own branded community
Facebook Comments - Facebook comments plugin lets people comment on content on the site using their Facebook account.
Zendesk - Zendesk is a beautiful, lightweight help-desk solution.