EasySocial!

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.

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!

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

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.

A full-featured open-source web site-creation package designed for the academic community.A single OpenScholar installation can host thousands of personal or project sites.

Google App Engine Social network.

Socibd is global platform that lets people easily build a social networking site in minutes.

SocialGO allows you to build a custom social network, whether you are a beginner or a seasoned developer. No software, hosting or coding required, as our team offers full support for your social networking site.

Ning is the social platform for the worlds interests and passions online. Millions of people every day are coming together across Ning to explore and express their interests, discover new passions, and meet new people around shared pursuits.

Plush is the most polished, user-friendly forum experience ever, featuring real-time discussions, beautiful design, an integrated blog, member directory, private messaging, paid subscriptions and a world-class mobile experience. All with absolutely no technical knowledge required and no plugins to install.