Proto.io, launched in 2011, is a fast way to prototype. The site is web-based with a drag and drop interface that’s easy to use. It’s a good simulator that includes “interactive touch gestures, screen transitions and animations”. With Proto.io, you can quickly design and visually plan out your vision. The barrier for communicating your idea for an app is lowered. Since the site doesn’t require coding ability, you’re able to plan out the UI/UX experience and customize how your app ideas. The site comes prepackaged with interactions made for mobile such as tap, swipe, click, and hold. There are also multiple transitions to choose from like slide and fade, editable templates, and other customizable features. It’s also collaborative with a multiple user feature and easy to view in HTML5 for testing on devices.
Check out their site and view their demo here.