Product Hunt Reviews Widget - Embed and encourage PH reviews into your product
DISQUS - Disqus is a global comment system that improves discussion on websites and connects conversations across the web.
PaidReview - Get paid for reviewing products
Hyvor Talk - The Best Commenting Platform For Your Website
Review Scraper API - Reviews from 50+ sites in JSON
Commento - A fast, bloat-free comments system to foster discussion on your website