Known!

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)

Google Sites is the easiest way to make information accessible to people who need quick, up-to-date access. 100MB/site free. People can work together on a Site to add file attachments, information from other Google applications (like Google Docs, Google Calendar, YouTube and Picasa), and new free-form content. Creating a site together is as easy as editing a document, and you always control who has access, whether it's just yourself, your team, or your whole organization. You can even publish Sites to the world. The Google Sites web application is accessible from any internet connected computer. »

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.

Octopress is a framework designed by Brandon Mathis for Jekyll, the blog aware static site generator powering Github Pages. To start blogging with Jekyll, you have to write your own HTML templates, CSS, Javascripts and set up your configuration. But with Octopress All of that is already taken care of.