Joomla

Joomla! is one of the most powerful Open Source (CMS) Content Management Systems on the planet. It is used all over the world for everything from simple websites to complex corporate applications. Joomla! is easy to install, simple to manage, and reliable.

demo:
http://demo.joomla.org/

Official site:
http://www.joomla.org/

Taiwan Offical site:
http://www.joomla.org.tw/