Pligg's Web 2.0 user interface gives your visitors a reason to come back to your site by making them decide on the site's content and giving them the chance to social network.

PHPizabi is a powerful social networking platform that's easy to install and use.

Elgg is an open source social networking platform based around choice, flexibility and openness: a system that firmly places individuals at the centre of their activities.

Blinkk is a social networking application inspired by digg, Newsvine and del.icio.us.

AROUNDMe is the perfect solution for you to bring people together around shared goals, activities and interests to form a shared knowledge network.

Create a site where users can rate and comment on stories or sites posted by your users--just like digg.com!

MySQLicious is a tool for mirroring del.icio.us bookmarks into a MySQL database.

Simplest comment framework. Add comments to your articles, blogs, etc... in seconds!

Ringside Social Application Server is the first open source platform that enables website owners to build and deploy social applications that operate with existing website content and business applications while seamlessly integrating with social networks such as Facebook.

OpenMicroBlogger is a multi-user messaging application that works like Twitter. It's a flexible communications tool that supports community by giving people control over their message stream, and it allows them to stay in touch from their mobile phone, laptop or desktop computer. The social-networking-style "I friend you and you friend me" feature makes it spam-resistant, and it is easy to install on any standard Web server.