BuddyPress is a plugin for WordPress that adds social networking features to your website. With BuddyPress you can create user profiles, groups, activity streams and more. It's an open source platform, which means you can use and customise it for free. Some of the features BuddyPress offers are

User profiles
Activity streams
Private messages
Friendship links

BuddyPress is designed to help you build a social network or community website using WordPress. It is a popular choice for educational institutions, businesses and other organisations that want to create a space for their members to connect and collaborate online.