I think the world needs an app especially for listening to audiobooks, because that's a special case needing different UI from listening to music. A purpose built app for listening to audiobooks needs a rewind 30 seconds button, like Audible has. It would also need special UI features for moving forward and back through the audio-- the normal slider method works really terribly when listening to a 4 hour long piece of audio where 1 pixel is like 7 minutes.