it is very easy for prototyping and also not everybody needs to be a designer.It also supports a variety of formats.

I like the ease-of-use with this platform. It offers many options - even with a free account - that allows you create wire framing.

Fluid UI has an easy to use interface. You don't need to be a designer to use this app, which is really great. The wide range of UI elements is able to cover almost any app. The output is extremely professional looking, and it's great to be able to demo your product on a phone. I would only use Fluid UI for earlier stage prototypes though because you can't upload your own images (unless you want to pay for a subscription)