With Flowshare, you can use any kind of image of what you want your app to look like, from a simple sketch to a detailed drawing, to create a detailed screen flow which can be shared with your potential users. With a Flowshare code, your users can try your prototype out on their own phones.
You get feedback in the form of heat maps of where people are clicking, allowing you to take design decisions from real data even before you release your product.