Movim!

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.

GNU social is a continuation of the StatusNet project. It is social communication software for both public and private communications. It is widely supported and has a large userbase. It is already used by the Free Software Foundation, and Richard Stallman himself.

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.

ZeroMe - Social network for the distributed P2P network zeroNet

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.

kune is a social network where you can communicate, collaborate and share between equals, using different web tools: documents, calendars, chats, wiki, messages, tasks, forums, barters.

Stay Connected. Be with Friends in Your World. Talk to Anyone in the World.

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

Viadeo is a professional social network used by over 40 million professionals in 226 countries worldwide.Our members consist of business owners, entrepreneurs and managers from a diverse range of businesses - both start-up and well-established. Every day Viadeo attracts more than 30,000 new members; 150,000 new connections are made and over 3 million profiles are viewed. In addition, Viadeo is available in English, French, Spanish, German, Portuguese and Italian.