The Jankó keyboard, named for inventor Paul von Jankó, compresses the standard 88-key piano layout into a thinner, four-row field of 264 keys. If this sounds like a solution to a different problem than the one addressed, you wouldn't be alone, but…
The Jankó Keyboard caused a stir at the time of its invention, in large part due to its unique look and the intelligent design behind the keyboard. American piano manufacturer Decker Brothers put the keyboard into production around 1891, and the Paul de Janko Conservatory of Music was established in New York around the same time. There was even a manual written by W. Bradley Keeler called How to Play the New Keyboard.
Despite all this, the Jankó keyboard never achieved wide popularity. Music educators were not convinced that the benefits of the new keyboard were enough to challenge the traditional keyboard. Few performers were prepared to relearn their repertoire on a new keyboard with entirely different fingering. Both reasons left keyboard instrument manufacturers afraid to invest in a redesigned keyboard which promised to have only marginal commercial success.
In the video embedded above, Paul Vandervoort demonstrates the Jankó.