Principle is one of my favorite UI animation tools. Not only is the learning curve to get started very small, but Principle is also immensely powerful when it comes to designing interactions. Its interface is not only similar to Sketch‘s interface (and thus already familiar), but it also integrates seamlessly with it as well, making the transition from static to interactive UI design very easy. Principle’s only down-fall, in my opinion, is that it only works for Mac computers. But Principle makes up for that inconvenience with their honest business model. Their 14-day free trial is actually a 14-day free trial (aka only the days you use the software are counted during your trial — the software doesn’t just disappear 2 weeks after you open it for the first time). The price point is also extremely reasonable, especially for what you get out of it. For a one-time payment of $129, you get free updates for a whole year after purchase, with unlimited use of the version of Principle you end on.
Anyway, I think you get the point — I’m a big fan of Principle. To show others just how easy it was to create animations and interaction design concepts, I started making tutorials.