Representatives for Tonara have contacted me a number of times about the Woflie app for iPad, which is by Tonara. Tonara is an app that follows you as you play, turning pages. Literature can be bought via in-app purchases.
Wolfie is geared for piano teachers and students, offering subscription based access to literature ($2.99 a week, $8.99 a month). I have blogged about a few other piano apps in the past (Piano Maestro and Flowkey, for example). While piano goes out of my normal sphere of influence for this blog (as the focus is generally on technology for classroom-based music education), some users may find the app of interest.
The download of Wolfie is free, and there are a number of resources that are given free to the user. The app is intended to be played with a live piano. There are a number of settings, such as practice, listening (with linked YouTube examples), evaluation, and more. There are levels of gameification, which has the potential to spark more user interest in the app.
If you teach piano or know a student that is learning piano, Wolfie is worth examining. Download the app and try the free content. I can't speak to the pricing for the “premium” subscription–you wil have to decide for yourself if the content warrants $9 a month ($108 a year). I worry about subscription plans for any app–they can add up quickly for a user, and materials you use aren't yours to keep. That said, these companies need ways to keep developing apps and to pay the bills.
And if you are a piano player, check out Tonara, too.