The app is related to the book’s content.

It helps readers to practise, focus, entertaining and…more…

It is a kind of extension for your book. It makes relation between the reader and the book (publishing company also) closer and more valuable. Using mobile app in time when book is put off is what increases the trust to the content you serve your readers.

Finally – continous playing with the content causes the words really can change a mindset and thinking. Isn’t what you publish books for?