Elgg is a powerful and award-winning PHP SNS(Social Networking Service) designed to deliver the building blocks that enable businesses, schools, universities and associations to create their own fully-featured social networks and applications. Elgg has been voted as the best open source social networking service in the year 2008.

Features of Elgg:
- Powerful Data Model: Elgg provides a powerful data model making the creation of different entities simple, yet flexible.
- Activity Streams: The granular activity stream API ensures your plugins can push the required content to your users.
- Plugin API: Use Elgg's powerful plugin API to build and add your required features.
- User Management: Elgg handles your user management and relationship requirements.
- Access controls: All objects in Elgg can have an access control level applied making granular access permissions possible.
- Web Services API: Expose functionality through the REST API by building a plugin and then either publish the API for other developers to build clients or provide your own.

Requirements:
- Apache web server
- PHP 5.2.0 or Higher
- MySQL 5.0 or higher is needed for data storage

What's New in This Version:
- Fixed the "http://" issue for profiles
- Auto-registering JavaScript files with calls to elgg_get_simplecache_url(). This helps plugin authors who forgot to register the file. This was exposed when we fixed a bug in 1.8.14.
- Added a helpful message for those sites that have a configuration error related to multiple URLs mapping to the same site. This was also exposed by fixing a bug in 1.8.14.
- Restoring sub-pages that have been missing after their parent page was deleted (pages plugin).
- Better revision support for pages (pages plugin).
- Adding nofollow to auto linked URLs to discourage spammers (thanks to Hellekin Wolf for pointing that out)
- Added browser caching for languages JS files