IT Managers Journal posted an article on Elgg
First, blogs moved from personal platforms to corporate tools. Now, wouldn't it be great to put social networking to work in your organization? Elgg is an open source application for creating social networks. It can be customized with themes and extended with plugins to work with other social networks or plug into an organization's existing wiki and forum boards. It lets users collaborate on projects within organizations or share notes within a university.Roll your own social network with Elgg