Social bookmarking

Social bookmarking is a way for internet users to store, classify, share and search Internet bookmarks.
Sites like reddit, Digg and the new Netscape portal apply social bookmarking to news items. In 2007, IBM announced plans to enter the social software market.
Some Exp:-
Bloglines
Blue Dot
Chipmark
del.icio.us
Digg
Diigo
Furl
GiveALink.org
Ma.gnolia
My Web
Netvouz (Allows both tags and folders for organizing bookmarks.)
Netscape
Newsvine
Reddit
Simpy
SiteBar (SiteBar bookmark server is open source software)
StumbleUpon