The plane guys know what I am talking about but for everyone else: A buddy box is used for training R/C pilots. Basically two transmitters linked togeather with the trainer's remote having master control over the system and the aircraft.
With our ground R/C's I don't this there has been a need before now. With the XO-1 I think this could come in handy. A noob (well a little past a noob) could drive this car fast with someone helping with minor correcting and there to take completely over if needs be.