SilverStripe

SilverStripe is a framework and content management system that runs on PHP5. Its goal is to give developers the ability to rapidly produce website features, and earnestly allow the average person to enjoy their time managing their site.

Its an open source (BSD) project being run from Wellington, and is the biggest one being headquartered out of New Zealand. We're a part of the Google Summer of Code programme that sees Google pay incredible hackers to work on features.