The Downloads In-App purchase activates the "Downloads" buttons on the Focused and Formula Calculator Lists. You can then download any of the Focused Calculators or Formula Calculators.
This gives you access to over 500 unique keys in just the Focused Calculators.
There are over 60 of these calculators. These links list the calculators currently available:
You can download as many of the calculators as you want with this purchase.