Looking for more IDEs, I have found this one:
http://www.qadram.com/products.php
The main (and big) difference with other IDEs is that allows you to develop visual interfaces like Delphi or Visual Studio, but for PHP and web applications.
It also says it's free and the component library it uses is LGPL.
It looks like it's not released yet, but looks promising, there are some nice videos to see it in action.