Part of PHP's power is actually found in the variety of open source (free to use) PHP based applications. I'm talking about things like blogs, web frameworks, forums, CMS' etc. I was just thinking, that a list of 'killer' PHP open source projects would be useful

There four on his list so far - WordPress, the Zend Framework, Drupal and Punbb.

To be totally honest about it, we've seen much of the good stuff coming out of the PHP world, in the last few years. PHP developers are leap-frogging ahead with regards to their level of skill and the quality of code they produce.