It almost pains me to write that title. I make apps to help students, I have about 12 of them on both Google and Apple and they are pretty good. None of them are the one I am talking about here though. Here is is all about Teach Your Monster to Read made, and made really well, by Usborne in the U.K. The links are all at the bottom for the app and website.
The best Free apps for ESL and Younger English Learners.