Marvel 4+

I love this app very much, and I am greatly pleased to give it a 5 stars rating. I encountered myself with a problem once. I spent over 3 hours one night creating images and linking them to create my prototype. Everything seemed to work perfectly fine and it even made it really fun to build a prototype. The major issue happened the next morning. As I woke up, eager to continue my project, I noticed that, although the images were still there, it was not working anymore so I went into the link editing mode and realized that ALL links where moved and resized... I wrote a review, which I have now updated, and reported the bug. It took them 14 hours to send a response. Within the next week a new update came out which fixed the bug. I am quite impressed with the amazing, fast, and efficient service that the people behind this app give to its users.
Hope this helped! And keep prototyping!

I usually use another program to prototype and wanted to try this. There's almost zero learning curve - it's so easy to use and the interface is uncluttered so it gets out of your way so you can quickly get down to work. You can play your app back on the screen, or even better, download the app onto your phone and you really get a good idea of how things are flowing. Don't hesitate, give it a try. I haven't used the commenting feature yet, but it seems pretty straightforward as well. You won't be sorry.

Marvel provides the right balance of simplicity and utility. The UI is easy to navigate and very intuitive. Transitions, simple icon library for typical functions and useful templates are all available- even in the free version. My only complaint and is that the web version is a little laggy at times but it’s not horrible. Another great feature is that your prototypes can be designed on the web and then run on your device. A great app/service that is uncluttered and allows you to focus on design.