Surely Wordpress is the Best open source system and then maybe joomla. I want to show you an example wordpress site that good designed;

http://www.arzunet.com

php is not much use for ope source. That requires real programming languages, NOT web scripting languages.

Maybe WordPress?

I am a CS student and I want to contribute to some open source project. I am good at PHP. Can anybody till me some good PHP projects to start with? I am absolute beginner to the open source so please let me know some easy projects so that I could learn the actual process of open source application development and I could later move on to some difficult one's.