Social Bookmarking
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The concept of shared online bookmarks dates back to April 1996 with the launch of itList.com. Within the next three years online bookmark services became competitive, with venture-backed companies like Backflip, Blink, Clip2, Hotlinks, Quiver, and others entering the market.
In 2005 and 2006, social bookmarking sites, such as del.icio.us, Digg, reddit, Furl, Ma.gnolia, Netvouz, and StumbleUpon became popular.
In a social bookmarking system, users store links to web pages that they find useful. These link lists are either accessible to the public or a specific network, and other people with similar interests can view the links by category, tags, or even randomly.
Most social bookmarking services allow users to search for bookmarks which are associated with given "tags", and rank the resources by the number of users which have bookmarked them. A collection of tags is often called a 'folksonomy', because it is a bit like a taxonomy or classification scheme, but is built from 'the bottom up' rather than 'top down'.