Connotea was a free online reference management service for scientists, researchers, and clinicians, created in December 2004 by Nature Publishing Group and discontinued in March 2013.
It was one of a breed of social bookmarking tools, similar to CiteULike and del.icio.us, where users can save links to their favourite websites.
ReadCube is a similar free service that offers storage, annotation and sharing tools specifically for scientific documents.
Connotea recognised a number of scientific websites and automatically collected metadata for the article or page being bookmarked, including author and publication names.
This function meant that it was possible to quickly retrieve the reference for a print article that had an electronic counterpart with a DOI.