This -centric open-source animation library looks promising.
👉 Motion on GitHub
Motion is an animation engine for gesturally-driven user interfaces, animations, and interactions on iOS, macOS, and tvOS.
I’ve been a little skeptical of open-source animation platforms since I had to toss out one app and then another as cocos2d morphed into cocosd2x and broke everything. Damn that x! But still, this looks cool. 👆
Via iOS Dev Weekly.