The mind-boggling reality is that a huge proportion of the world’s hit songs are built upon the same four chords. Don’t believe me? Just listen to this medley by comedy rock band, ‘Axis Of Awesome’: ...

(And for me, because I just described myself, as well.) It’s called 4 Chords, and it’s a karaoke app for guitar. This app for iPhone and iPad starts by letting you choose from a library of ...