Elgg is an open source social networking engine that provides users with the ability to create fully customizable social environments and applications. It was launched in 2004 and aims to provide developers with a powerful framework on which to build all kinds of social features and functionality.
Some of the key features and capabilities of Elgg include:
Overall, Elgg provides a full-featured and flexible framework for building a customized social environment, allowing users to blog, share files and photos, create groups, and expand functionality through plugins.