About diigo.com

An abbreviation for the "Digest of Internet Information, Groups and Other stuff," Diigo is a social annotation service that lets users add highlights and notes _in situ_ to any web page.

These overlayed comments made through Diigo can be made either public or private;

other Diigo users can then read public comments and reply/interact to comments.

Diigo combines aspects of social bookmarking, full-text search, annotations, tagging, and sharing. A browser plugin allows you to share your annotations directly with others, and you can save annotated pages to numerous other bookmarking services as well.