“PHP: The Right Way” – A Guide For Writing Better PHP Code
There are lots of information on the web that PHP developers make use of. However, many of them are outdated and can guide anyone to write "bad code".
"PHP: The Right Way" is a very detailed and free documentation of PHP's best practices to help anyone write better code.
There is no standard way of writing code and the website aims to show the generally accepted practices and alternatives. Also, there are lots of links to authoritative tutorials on the web.
It has topics from the setup of PHP to the basics, security, caching and much more.
Simply, a must-check guide for any PHP developer. And, you can help the documentation to be improved further (it is hosted on GitHub).