PHP: Hypertext Pre-Processor (PHP) is an open source software language used on web servers. It’s a very common language with a large number of open source projects built with the language, for example, Drupal, WordPress, and many others.
Sandbox
These tools let you code on your phone, tablet, or desktop computer.
Support
Where to get support as you code and encounter error messages and bugs in your applications.
PHP.net Getting Help
http://www.php.net/support.php
Stack Overflow
http://stackoverflow.com/questions/tagged/php
Google Groups: comp.lang.php
https://groups.google.com/forum/#!forum/comp.lang.php
Tutorials
Hands on tutorials, as well as the home page for the language and documentation.
PHP.net
https://www.php.net
http://www.php.net/docs.php
W3Schools PHP Reference
History
The history of the language.
About PHP
https://en.wikipedia.org/wiki/PHP
Implementation
How to use this language on the internet and the real world, available to end users and customers.
In the Wild
How this language is used on the internet and in the real world.
Popular PHP Open Source Projects
https://github.com/languages/PHP/most_watched
https://www.wordpress.org
http://symfony.com/
http://drupal.com/
http://ellislab.com/expressionengine
http://ellislab.com/codeigniter