They are a kind of keyboards made to explore new scales for advanced musicians; but also there are some others intended to make learning easier.

There is the Janko; which keeps a plain structure for each note. If you some time tried to learn piano, you will understand how interesting is this  keyboard; it is possible to play every major scale learning it only once instead of 12 times as in standard keyboard.

In this link you can play around with a simulation of this. To play major scale, start by clicking the red buttons. There are also some real keyboards sold by some brands; and also an ipad app called musix.

You may find in this same link other kinds of experimental keyboards