One of the world’s most famous examples of a public service Social Machine, Wikipedia is an example of how Social Machines evolve to become a vital, knowledge sharing public service.
Knowledge Sharing Social Machines
Stack Overflow is a question and answer site for professional and enthusiast programmers. Stack Overflow is the flagship site of the Stack Exchange Network, created in 2008 by Jeff Atwood and Joel Spolsky as a more open alternative to earlier Q&A sites such as Experts Exchange. The name for the website was chosen by voting in April 2008 by readers of Coding Horror, Atwood's popular programming blog.
Github was founded in 2008, and by 2011 became the most popular open source code repository, beating competitors sourceforge and google code. Github provides social networking functionality such as feeds, followers and the network graph to display how developers work on their versions of a repository. What Github did differently: it made commits/repositories highly visible - an "implicit" extrinsic motivator.
reddit is an entertainment, social networking service and news website where registered community members can submit content, such as text posts or direct links. Only registered users can then vote submissions "up" or "down" to organize the posts and determine their position on the site's pages. Content entries are organized by areas of interest called "subreddits".
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 ]
Delicious (formerly del.icio.us ) is a social bookmarking Web service for storing, sharing, and discovering bookmarks. The site was founded by Joshua Schachter in 2003 and acquired by Yahoo! in 2005. By the end of 2008, the service claimed more than 5.3 million users and 180 million unique bookmarked URLs.