Julie Delanoy
Julie Delanoy reviewedPrincipleAnimate your ideas, design better apps
 RecommendedPros: 

Really simple to use. No need for a tutorial to start :)

Cons: 

The preview window is often over the main window, not easy when you're working on a laptop.

I use Principle mostly for quick demos when I try to communicate interaction ideas with my teammates. Principle is very good for this if you're not trying to create something too fancy but really want to share your ideas. Word to the makers: Keep the good work!