This Hillel Wayne post [0] mentions a startup called Sketch.systems [1], which I think is sort of like what you said? It's not just a UI prototype; you build a

This Hillel Wayne post [0] mentions a startup called Sketch.systems [1], which I think is sort of like what you said? It's not just a UI prototype; you build a model of the underlying state of the system as you transition from screen to screen. 0: https://www.hillelwayne.com/formally-specifying-uis/ https://www.hillelwayne.com/formally-specifying-uis/ 1: https://sketch.systems/ https://sketch.systems/