Symfony - PHP Web Framework
Symfony is a Web Application PHP framework which follows the model-view-controller (MVC) paradigm. Symfony is the leading PHP framework to create Websites and Web Applications. Built on top of the Symfony components. Symfony provides an Architecture, Components and Tools for Developers to build complex Web Applications faster by minimizing repetitive coding tasks.
Symfony has huge community, IRC usually has helpful for Symfony Developers.
Symfony in Drupal 8:
These are the following Symfony components included in Drupal 8
HttpKernel provides the building blocks to create flexible and fast HTTP-based frameworks.
HttpFoundation defines an object-oriented layer for the HTTP specification.
Routing associates a request with the code that will convert it to a response.
The Symfony EventDispatcher component implements the Mediator pattern in a simple and effective way to make your projects truly extensible.
ClassLoader loads your project classes automatically if they follow some standard PHP conventions. The ClassLoader object is able to autoload classes that implement the PSR-0 standard or the PEAR naming convention.
DependencyInjection manages your services via a robust and flexible Dependency Injection Container.
Twig is a modern template engine for PHP
This component is based on the JSR-303 Bean Validation specification and enables specifying validation rules for classes using XML, YAML, PHP or annotations, which can then be checked against instances of these classes.
Translation provides tools for loading translation files and generating translated strings from these including support for pluralization.
Process executes commands in sub-processes.
With the Serializer component its possible to handle serializing data structures, including object graphs, into array structures or other formats like XML and JSON. It can also handle deserializing XML and JSON back to object graphs.
YAML implements most of the YAML 1.2 specification.