People told Andreas Raptopoulos it was a crazy idea when he and a few of his colleagues at Matternet started talking a couple of years ago about creating invisible highways for drones to deliver critical goods such as medicine in the developing world. First off, drones do not have the best reputation in certain parts of the developing world. But one billon people have to deal with lousy or nonexistent roads. And billions more in urban areas are tormented by traffic congestion. So Raptopoulos and his team forged on.