I have humhub installed on a site and for the purpose it is great. It is different in architecture from UNA as it is based on Spaces. I like that you have some useful plugins that installs easily and it has some cool chat systems that you can use with one click install.

mine is at http://musthavepets.com where I am testing it and working on a few things.

Andrew Boon gave a good summary above.

Best thing to do is install them and try them out.

Try to find Oxwall or its branch Oxwall Engine.  It was my favorite Social Network CMS until they stopped development and went commercial with skadate.

There is also Jamroom, Drupal, Joomla or WP with their community builders and numerous plugins.