Topic: Building a social networking site

Hi everyone was wondering if I could get some guidance.

Im looking to start to develop my own social networking site, ive made some basic rails apps and not bad coder in Ruby, however with the business idea I have I want to get a site up and running as quickly as possible.

I have been doing some re-search and have found a load of off the shelf ROR sites/plugins that basically give you a fully functional facebook type web app.

I want to use one of these, but one that would be the easiest to hack and customize, especially one with a really good 'group' system, does anyone have an opinion on which one of these open source rails apps are the best for  my requirements?