Body is the interface.
Mind is the content.
Languange is the API.
Human interacts with its surrounding through the body.
Human without mind is not functional.
Human exchanges information through language*.
The interface can be tweaked, but the content is still the king.
The more API you provide the more platform can understand you.
The most useful app is the app with a purpose. It is made to solve a problem and it solves the problem well.
*Sign language, oral language, typed language, whatever.