In case you hadn't heard by now, the symfony project's components sub-project of the main framework has gotten its own website:

Some time ago, I have introduced the new "Symfony Components" project. It is a sub-project of Symfony that aims to give more importance to some of the great libraries we have developed for Symfony. [...] Today, I am happy to announce that the Symfony Components now have their dedicated website.

Each of the current components (YAML, Event Dispatcher, Dependency Injection, Template - though the last three are "coming soon") have documentation, info about the API, examples of how to install and use it and how to give back to the code for the component directly.