This website is built with TYPO3, which is a free and open source content management system. It is written in PHP and is released under GNU GPL. It is as popular as WordPress but the majority of its users are confined in Europe.
I suggest you to install TYPO3 and give it a try if you are looking for a good content management system. The learning curve for TYPO3 is steep (relatively steep !!) but once you get the know-how, you will enjoy each and every part of TYPO3.
The URL to TYPO3 is http://typo3.org/