EFL is a collection of libraries that are independent or may build on top of each-other to provide useful features that complement an OS's existing environment, rather than wrap and abstract it, trying to be their own environment and OS in its entirety.

This means that it expects you to use other system libraries and API's in conjunction with EFL libraries, to provide a whole working application or library, simply using EFL as a set of convenient pre-made libraries to accomplish a whole host of complex or painful tasks for you.

See EFL for more detail