The Smartphone
Apple's iPhone merged the phone, the camera, the map, the music player, and the Web into one glass rectangle, and within fifteen years most adults on earth carried one. It put more computing power in a pocket than the Apollo program commanded, connected billions of people who had never had a landline, and rebuilt how humans meet, work, argue, and pay. It also made attention the product: the same device that put the world's knowledge in every hand made every hand trackable, and made a small number of companies the arbiters of what billions of people see.
A new way to record or transmit information lowers the cost of copying ideas and reorders who holds knowledge and power.