digg

What started as an experiment in the fall of 2004 is now a major online presence with an estimated 40 million monthly users. Kevin Rose's concept of a user-controlled community that votes to \digg up what links that they collectively deem important, or bury down those of little interest, has been successful in part because of the company's ability to adapt and add new features. [via Mashable’s History of Digg ]

Input: 

Primary: Users submit links to news stories
Secondary: Users vote up and down stories depending on level of interest.  This vote is weighted by people’s reputation; users with more reputation influence stories more heavily.

Human Computation Elements: 

Humans submit new content, thereby serving to feed the system, and rate existing content

Category type: 
Knowledge Sharing Social Machines