They’re online tool for shared articles and bookmarks. People suggest links to things they like for other people’s benefit…

del.icio.us – http://del.icio.us/

del.icio.us is a social bookmarking website — the primary use of del.icio.us is to store your bookmarks online, which allows you to access the same bookmarks from any computer and add bookmarks from anywhere, too. On del.icio.us, you can use tags to organize and remember your bookmarks, which is a much more flexible system than folders.

reddit – http://reddit.com/

Reddit is a source for what’s new and popular on the web — personalized for you. Your votes train a filter, so let reddit know what you liked and disliked, because you’ll begin to be recommended links filtered to your tastes. All of the content on reddit is submitted and voted on by users like you.

Digg – http://digg.com/

Digg is all about user powered content. Every article on digg is submitted and voted on by the digg community. Share, discover, bookmark, and promote the news that’s important to you!

Clesto – http://clesto.com

Is also a social bookmarking site.