Symfony, one of the most popular PHP frameworks around, is sharing several standalone PHP classes (under the Symfony Components website) which can ease the job of a PHP developer.
They don’t require Symfony to be used & can be used with any PHP code.

Currently, 3 classes are ready to be used:

YAML
It parses YAML strings and converts them to PHP arrays. It can also converts PHP arrays to YAML strings.
Event Dispatcher
It’s a good way to make your code more flexible. It’s also a great way to make your code easily extensible by others.
Symfony Event Dispatcher is a PHP library that provides a lightweight implementation of the Observer design pattern.
Dependency Injection
It provides a lightweight and robust Dependency Injection Container for classes that implements the Dependency Injection pattern.

And, 2 new classes are on the way:

  • Templating
  • Request Handler
All the code provided is very well-documented & totally free to use.