Apple Xcode Playgrounds are perfect for quick and dirty exploration of iOS, macOS, and general software development explorations... ok, perfect might be a little to strong a word here!
I'd like Playgrounds to include better debugging tools and the ability to compile to standalone, sharable applets. There is a ton of functionality in Playgrounds but it's hard to marshal because Xcode doesn't make building a sophisticaed playground as easy as an iOS app! But if/when Apple addresses these minor shortcommings, I'd probably just do Playgrounds all day long.
But enough grousing!
Exploring the SDK what Apple provides with alerts actions
Exploring dynamic UI behavior animations provided by UIDynamicAnimator (from a WWDC contest a few years back)
Swift 5 features make FizzBuzz too easy by half!
Swift functions that apply functions to transfom value (with Generics)!