Diigo is a social bookmarking website which 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 a special link forwarded to someone else. The name "Diigo" is an acronym from "Digest of Internet Information, Groups and Other stuff".