Wikipedia
BuddyPress
BuddyPress is an open source social networking software package owned by Automattic since 2008. It is a plugin that can be installed on WordPress to transform it into a social network platform. BuddyPress is designed to allow schools, companies, sports teams, or any other niche community to start their own social network or communication tool.
BuddyPress inherits and extends upon the integral functional elements of the WordPress engine including themes, plugins, and widgets. As it is built on WordPress it is written using the same primary technologies, PHP and MySQL.