Digg is a user driven social content website - users comment on and rate news stories.
Common Craft "made this video because we want others to feel the power of social bookmarking and how it works to make web pages easier to remember, organize and share."
Diigo is two services in one -- it is a research and collaborative research tool on the one hand, and a knowledge-sharing community and social content site on the other. As you read on the web, instead of just bookmarking, you can highlight portions of we
Social Bookmarking addresses a community-or social-approach to identifying and organizing information on the Web. Social bookmarking involves saving bookmarks one would normally make in a Web browser to a public Web site and "tagging" them with keywords.
XtLearn is a portable collection system for education, allowing you to gather resources from any source, edit collections, and share them with both learners and other educational practitioners.