This is a great example of things that had a limited availability, being made obsolete by progress.
The plugs that this is sized to take were the "standard" before 1960. A very common receptacle was a "triplex:" three receptacles in a single-gang box. Triple-switch devices were also made.
In the '50's, receptacles assumed today's shape & size. Not too long afterwards, the ground pin was introduced.
There were also receptacles that had terminals for antenna wires.
Only a few years before the advent of the GFI, there was a big fad of using low-voltage devices in kitchens & baths; you could hear the relays clicking in the walls.
