This is present continuous, as you correctly said, but it is present continuous for future use.
You use the same construction as with PC but then add a time in the future.
I am driving to London (i.e. I am in the car).
I am driving to London this evening/ tomorrow/ at the weekend.
(I have made arrangements to drive to London but Iam not yet in the car).
So, for your example:
What are you doing? (PC)
What are you doing this evening? (PCFU)
It is a Simple Future, often called the Diary Future.