Best of all of the Bundle Packs is this one, at least so far.

This has a wide selection of ambient loops and optional binaural tones, including progressive ones.
I am not fond of all of the loops, but this app has the ones I have grown to enjoy most.
The "focus" tones start low and slowly raise from 12 to 14Hz. It seems to do what it claims, but perhaps that is the placebo effect.
I bought the app originally because of the free sample apps offered. I wanted to get a large selection of the loops along with supporting the developer.

The developer is also very responsive.

DeadWriter about Pure Sleep | AmbiScience™ • Binaural & Isochronic Ambient Sleep Utility