【正】An app that does nothing but send a simple notification of"Yo"to recipients is the most popular app right now in the US.Created in just eight hours by Or Arbel,a32-year-old app developer from Tel Aviv,Israel,Yo claims to be the"simplest and most efficient communication tool in the world".With a single tap,users can send the word"Yo"to one another in a voice notification and nothing else.Arbel enthused about his app in an interview