FYI it's built using Swift and ReactiveCocoa. They put up all the dependencies licenses in Settings so I made a list of the packages they use https://gist.github.com/ropiku/b259f35060a40eab1597.
So the fact that reactive cocoa tries to hide the notion of state transition makes me wonder how you can then deal with UIKit views animations api ( collection flow animations or tableview begin updates, no to mention view controllers interactive transitions).
I've wondered if using a future based api for view animations wouldn't be a solution..