schnack is an awesome, ad-free, open source Disqus clone that comes with a very minimal, hackable code base.
Hosted commenting that's painless to embed, a pleasure to use, and a breeze to moderate.
MyTwoCents is a Chrome extension that adds a comment section to any website you want. The idea is to offer discussions on sites where there originally is none or where comments are disabled, .e.g. on news sites or on Netflix or live sports streaming or anywhere you want to add your two cents :)
CMMNTZ is a next-generation application utilizing technology to fix what is broken with online commenting: high moderation costs, trolls, spam, flame wars, monopolizers, and vitriol. Users and online publishers will both benefit.