- Definitely Principle! Export your Artboards and just open them in Principle - done! Lots of animations, interactions, lots of options, just a great tool for putting together a prototype. UI is quite similiar to sketch, so everything feels familiar if you are a longterm sketch-user. At 129$ you get the perfect tool for turning your sketch artboards into animations and interactions.
Kite Compositor is my new go-to prototyping tool. As a long time iOS developer, most of my prototyping was just done in Xcode because I had complete access to Core Animation. Kite, unlike other tools, is built on top of Core Animation and exposes all (or most) of its features directly. As a result, the animations it builds are almost guaranteed to look exactly the same on device.
Beyond that, it's just a well-designed app. As with most professional applications, the UI takes a bit of poking around at first to figure out how to do everything, but after just a day of playing with it, I became familiar with most of its capabilities.
Amazing tool for UI and learning Core Animation.