A project of the Elgg Foundation, Elgg is a free open source social networking engine licensed to users under the GNU Public License v2. The REST Elgg API allows developers to integrate Elgg and offer new apps for it. To give a sense of its size, 1,646 plugins have been created so far by the user community, with nearly 3 million downloads. Examples of plugins include blogs, forums, social bookmarks.
Facebook has updated the Facebook SDK 3.1 for iOS, adding the ability to integrate Facebook in iOS 6 as well as other new features. Apple has added several new native features in iOS 6 including Auth dialog and view controller (share dialog). The Facebook SDK supports the use of these APIs.