Framer Studio is a prototyping app for OS X, built on FramerJs, an open source JavaScript framework used for rapid prototyping.
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Pros
Pro CoffeeScript integration to define animations
Framer uses coffeescript for defining animations. CoffeeScript has a low learning curve and as such it can be learned easily even by non-programmers.
Pro Multiple device support
Framer supports animation and interaction prototyping for multiple devices, ranging from desktop apps to web apps and mobile platforms. There are already 8 pre-installed devices to choose from, or developers can create their own setup quickly.
Pro Photoshop & Sketch integration
Framer is integrated with Framer Generator, which allows developers to import layers directly from Adobe Photoshop and/or Sketch.
Pro Instant visual feedback
Framer Studio offers and instant preview of the animation that is currently being made.
Cons
Con Coding required
Framer Studio uses CoffeeScript for prototyping the UI of an app. This can be a problem for designers who don't know CoffeeScript since they would be forced to learn a new programming language in order to use Framer.
Con Mac only
Framer Studio is only supported for Mac. There is no version for Windows or Linux.