For me, Garage Band's most outstanding features are, you can pick a scale and all the keys on the keyboard (or strings on the guitar) are coherent to the scale you picked. Moreover, you can never miss the rhythm if you choose; whenever you tap on screen, the software automatically catches the rhythm.
I need a piano app that has the first feature. If it also has the second one, that would be an enormous app. But I know that is not the case. Besides "Blues Piano" (it has very, very bad response time), do you know such apps.
Not highlighting the keys that belong to the scale, but disappearing the rest.
Edit: I have tried Walk Band, but the features I have written are both not present.