Slevomat Coding Standard for PHP_CodeSniffer provides many useful sniffs

Helps you install the appropriate browser driver

The Symfony PHP framework

Twig, the flexible, fast, and secure template language for PHP

A static analysis tool for finding errors in PHP applications

Dependency Manager for PHP

A bundle that you can use to define and enable/disable features.

A library that provides strict typed collections in PHP.

A PHP Library for resolving, visualizing and validating composer dependencies within a repository. Works within a monolithic repository as well.

A simple package for running multiple processes within a PHP process

English PHP documentation

Provides commands to validate dependencies within a monolithic repository structure

The PHP Interpreter

All PHP functions, rewritten to throw exceptions instead of returning false

Doctrine Object Relational Mapper (ORM)

A library that provides strict value objects in PHP.

A library that provides a basic form flow implementation.

The Symfony documentation

A library that provides the tree node functionality.

A library that provides a secure way to cast variables in PHP.

A library that dynamically maps properties between objects.