Lake is an iOS app that allows designers to prototype mobile applications with complex functionality at low cost. By allowing designers to manipulate digital elements (e.g., maps, images, etc.) in real-time in the same manner as the Wizard of Oz technique in paper prototyping, Lake eliminates the need to create pre-canned interactions through patches or hotspots.

For example, a designer could prototype a Snapchat feature that adds dog ear overlays to humans by adding a camera element to their prototype, and in response to seeing the tester’s live camera stream update, drag two dog ear images to cover their ears on the fly without having to write a complex face tracking algorithm.

Wizard of Oz digital prototyping gives designers the same benefits that patch-based tools provide, at the same low cost of hotspot based prototypes.