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Diaspora is a federated social networking service, designed to be a more privacy-aware alternative to Facebook . Share what you want, with whom you want.

Friendica is a distributed social network application which runs on commodity hosting platforms - PHP/MySQL/Apache. (If you can install Drupal or Wordpress you can probably install Friendica)

HumHub is a free social network software and framework built to give you the tools to make teamwork easy and successful.

Social networking in a box. Build a social network for your company, school, sports team or niche community all based on the power and flexibility of WordPress. Install BuddyPress directly through your WordPress dashboard plugins page, or download it manually from the WordPress.org plugins repository.

Libertree is free, libre, open-source software which is intended to provide a way for people to create their own social network. Libertree social networks can be free from commercial influence and manifestation, such as behaviour tracking, user profiling, advertising, data mining and analysis, and covert information filtering.

Yammer is revolutionizing internal corporate communications by bringing together all of a company’s employees inside a private and secure enterprise social network. Although Yammer is as easy to use as consumer products like Facebook or Twitter, it’s enterprise-grade software is built from the ground up to drive business objectives.

SPIP is a publishing system for the Internet in which great importance is attached to collaborative working, to multilingual environments, and to simplicity of use for web authors. It is free software, distributed under the GNU/GPL licence. This means that it can be used for any Internet site, whether personal or institutional, non-profit or commercial.

The award-winning Open Source Community software for Joomla. JomSocial is a powerful social networking software, loaded with plenty of social network features to empower your community such as entrepreneur circles, gamers clubs, hobbyist communities, artist fan pages and a lot more!

Noosfero is a web platform for social networks with blog, e-Porfolios, RSS, thematic discussion and events agenda in the same system.Get to know, use it, participate and contribute to this free software project.

Social Network For Joomla to grow your communities with the least time.

Elgg is a leading open source social networking engine which can be used to power your social network.