One of the strengths of Symfony2 lies in its components; they define the building blocks of the framework and they can be used as standalone libraries:

For instance, Silex, a micro-framework for PHP 5.3, is based on the Symfony2 components; Sismo, a simple continuous testing server, has been built using many components as well.

The Symfony2 components have been available on Git for quite some time now, and as of today, I'm really excited to announce that they are also installable via the brand new Symfony2 PEAR channel, powered by Pirum of course.