Delicious

Delicious is a service of social bookmarking web. Allows you to add markers that typically were kept in browsers and categorize a labeling system called folksonomies (tags). Not only can store websites, but also allows sharing with other users of del.icio.us and how many have saved a particular link in your bookmarks.
One of the secrets of his success is perhaps the simplicity of its interface, using very simple HTML and a set of readable URLs. It also has a flexible web syndication service through RSS and an API that allows applications to work quickly to del.icio.us.
The service is in operation since 2003, maintained primarily by Joshua Schachter and Memepool support. On December 9, 2005 was acquired by Yahoo. The company decides to keep it independent and spear yahoo bookmarks, using the API to import links from delicious (though not vice versa).

http://www.delicious.com/