ELGG is a powerful and leading Open Contentment Management System(CMS) for Social Networking. It is an Open Source Platform managed by elgg.org and community developers. Elgg is very flexible engine application designed to replicate and even enhance the most advance features of existing social networking communities like Facebook, MySpace and others. It is relatively new web application released on mid 2008 but was under development since 2004. It's latest version is 1.6.1. Elgg is extremely lightweight,easy to use and user friendly whose main features are highlighted below:
 
1. Social graph functionality (relationships between users and other users, objects and sites
2. Multiple sites (or applications) per installation (coming soon)
3. Easy internationalisation support
4. System-wide, tag-based searching across all content and users
5. Fine-grained access controls
6. Multiple views, allowing for mobile applications and embeddable widgets as well as the traditional web browser view
7. Event, plugin and widget APIs
8. RSS, FOAF, XFN for content syndication
9. OpenID, OpenSocial
10. Open Data Definition and an increasing number of data portability formats for import / export
11. An extensible RESTful API, with results in JSON, serialised PHP or XML
12. AJAX through jQuery and user-definable callbacks.
#.Easy extension for use with caching systems such as memcached, for increased system performance.
14. Use of multiple database connections for scalability (still in development).
 
               Plugins and other resources are jointly maintained by elgg.org and elgg community and are easily available which is extreamly important for an Open Source platform. Elgg comes with advanced user management and administration, social networking, cross-site tagging, powerful access control lists, internationalisation support, multiple view support (eg cell phones, iPhone), an advanced templating engine, a widget framework and more. Elgg is great application but there are also some features that I didn't liked. For example it does not give as Control over your project as a administrator over you site and its user as you like and which are there on other CMS like Drupal, Joomla and others. There are not many users and developers working on this project so the There are not many contribution for plugins and totorial material. Here is a sample site created by us under NOSK Labs. It is still in its alpha phase and is used for testing purpose. please visit this site and register there. There are lots of things to be done so please post your comment here.  http://demo.nosk.org.np/hamigaffadi/