In response to the number of questions (and popularity) of his previous information about the Aura framework and how it compares to Zend Framework 2 (and Symfony2), Paul Jones has posted more about its decoupled nature and how the frameworks compare.

Being able to use Symfony2 components or ZF2 modules is not quite the distinction I am making. The distinction is that all Aura packages (with the exception of the Framework package) are completely independent, and have no cross-package dependencies, whereas at least some of the components from Symfony2 and ZF2 have dependency requirements.

He illustrates the point with a common task across all of the frameworks - input validation and filtering. He starts with a look at how to handle it in Zend Framework 2 (with Zend/InputFilter) with the list of packages also pulled in by the Composer install. He does the same with the Symfony2 "Validator" package and mentions the other packages needed to execute its tests. Finally, he looks at Aura's "Aura.Filter" component and it's lack of dependencies (and that its tests can be executed immediately).