Hypothes.is 
is a 501(c) open-source software project that aims to collect comments about statements made in any web-accessible content, and filter and rank those comments to assess each statement's credibility. It has been summarized as "a peer review layer for the entire Internet." - wikipedia
As of December 2017, Hypothes.is is the 113,770th most popular site on the Internet according to Alexa.com.