Hypothes.is will be a distributed, open-source platform for the collaborative evaluation of information. It will enable sentence-level critique of written words combined with a sophisticated yet easy-to-use model of community peer-review. It will work as an overlay on top of any stable content, including news, blogs, scientific articles, books, terms of service, ballot initiatives, legislation and regulations, software code and more-without requiring participation of the underlying site.
http://hypothes.is/what-is-it