The electric motor, in all its guises where electricty produces mechanical motion. The industrial revolution was restricted to places of work and shared production until the relatively small and clean electric motor enabled the adoption of its bounty into the home; for instance, refrigeration, automated cleaning, cooling, better heating, entertainment, mass data storage, home medical care, and more comfortable personal transportation.
True, many of these aspects were present in the home with simpler technologies (e.g., gravity driven water flow, convective air flow), but it was the electric motor which made them pervasive.
The change in our western lifestyle has been profound and has completely changed our expectations of how our bodies should fit with our surroundings.
A question: what will it take for the computer revolution to truly enter our lives in the way that the electric motor has enabled the industrial revolution to do so?