You can't add new songs or exercises to the library in this version of the app. The songs are made by transcribing the original songs (check out for example Cantaloupe island or Giant steps) so the sound can be as close as possible to each song. It's a "handmade" app! Apart from this, there is the polyrhythmic part of the app, which is the most important here. For each song, we choose the polyrhythmic patterns, basslines and piano comping that sound well when you mix all this stuff together (like for example in the Randomize all function). This is necessary so you can practice polyrhythms in the right context.