On the SitePoint PHP blog today there's a post introducing you to the concept of building a framework with Symfony components, using only the ones you need from the Symfony framework ecosystem to create a customized framework to fit your needs.

You’ve probably met Symfony in your PHP career – or have at least heard of it. What you may not know is that Symfony is, at its core, composed of separate libraries called components, which can be reused in any PHP application. For example, the popular PHP framework Laravel was developed using several Symfony components we will also be using in this tutorial. The next version of the popular CMS Drupal is also being built on top of some of the main Symfony components. We’ll see how to build a minimal PHP framework using these components, and how they can interact to create a basic structure for any web application.

He covers some of the main parts of the framework, how to grab the components that will help with some of the common functionality and integrating them to work together. He uses the HttpFoundation, HttpKernel, Routing and EventDispatcher (along with their own dependencies) to create a simple example that will respond to a few different route requests.