https://matias.store/products/half-keyboard
The Matias Half Keyboard is based on a theory that our minds mirror each hand, so by holding the space bar to access the missing half keyboard, we already know what to do. I was skeptical. Recognizing that we're modal (do we even recognize that telephone keypads and numeric keypads are different, or do we just use them without thinking?) I decided to learn Dvorak on the half keyboard while continuing to use QWERTY on my full keyboards.
One day, on a lark, I tried Dvorak on a full keyboard. I could, easily. The mirror theory holds.