An interesting way of executing Application Services is through a Command Bus library. A good one is Tactician. From the Tactician website:

What is a Command Bus? The term is mostly used when we combine the Command pattern with a service layer. Its job is to take a Command object (which describes what the user wants to do) and match it to a Handler (which executes it). This can help structure your code neatly.

— our Application Services are the Service Layer, and our Request objects look pretty much like Commands.

Fair enough — our Application Services are the Service Layer, and our Request objects look pretty much like Commands. Wouldn't it be great if we had a mechanism to link all the Application Services, and then based on the Request, execute the correct one? Well, that's actually what a Command Bus is.