Over the Holidays, I've been building a new prototyping tool to help with designing iOS apps, called Tweak. It's essentially an animation/interaction prototyping app, built on top of UIKit.
Working with tools like Quartz Composer and Framer.JS is generally amazing, but there's always that moment once you have things just right in your prototype that you have to play the interpretation game with developers to actually implement things. Tweak aims to get rid of that translation process since you're tuning things with actual UIKit code. The values you use in a prototype are the real values and code that can ship in a production app.
Stay tuned for more.
Shout out to @[1005:Jorn van Dijk], from whom I stole the lovely animation icon :)