The Pain27 keyboard has only 27 keys. There's one for each letter of the alphabet, and a space bar.
The pain27 is an open source keyboard project to make an easily usable, yet completely and utterly unusable qwerty keyboard with all the letters of the english alphabet, a spacebar, and nothing else. Supports cherry mx style and smk switches, through hole leds for backlighting, rgb underglow, and only requires a pro micro for programming.
Technical usability is conferred by holding down particular keys to trigger alternate layers. Hold and release "z", for example, and it will instead have shifted the board.
Compare to my design for the "Cormac", a keyboard useful only for writing novels by Cormac McCarthy: