Diigo

Diigo is a social bookmarking website that allows signed-up users to bookmark and tag Web pages. Additionally, it allows users to highlight any part of a webpage and attach sticky notes to specific highlights or to a whole page. These annotations can be kept private, shared with a group within Diigo, or be forwarded to someone else via a special link. The name "Diigo" is an acronym from "Digest of Internet Information, Groups and Other stuff".