Buddypress

Customizable social networking plug-in for Wordpress

BuddyPress is an open-source social networking software for Wordpress websites. Designed for schools, companies, sports teams, and other niche communities.

Notes:

Start your own social network or online communication tool
A social network tool that is easy to integrate and use within Wordpress
Users create and update their own profiles, send private messages to one another, befriend and de-friend each other, form and join groups, participate in forum discussions, and more