Something I missed when moving from AS3/JS to iOS development was the greensock tweening libraries.
Apple has some easing equations but not the extensive Penner-style library. I have found some easing classes written in Objective C and decided to take up the challenge to port a SpriteKit tweening library to Swift. I liked SpriteKit-Easing by budding monkey and have created a Swift version ‘SpriteKitEasingSwift‘.
Using this library you can generate a custom tweened property in an SKAction, and run the tween just like any other SKAction. I hope to add more properties that can be tweened in the future.