I've got an idea for a mobile app. It will be called "4:33" in honour of the John Cage composition.
Like the John Cage composition, it won't have any actual content. It will merely show a blank white screen for 4 minutes and 33 seconds, during which you listen to the sounds going on around you.
It would be amazing to have 30 people on a train seemingly glued to their phones but in actuality deeply tuned into their environment.