We need to select a social networking platform to build off of. Dolphin is a good PHP-based platform we could start with. The product website is at: http://phpdolphin.com/ They have a demo site but you have to register to see anything so it's hard to really tell.
I don't see any kind of group functionality or the other main features of the other products we're looking at.
People would be possibly familiar with the interface.
This content is created by the open source Your Priorities citizen engagement platform designed by the non profit Citizens Foundation