A previous HN thread about the swift-compiler-crashes project: https://news.ycombinator.com/item?id=9020206
One tweet and the bug is fixed within a couple of hours. Wow!
Found that issue while working on the Pythonic.swift project: https://github.com/practicalswift/Pythonic.swift (btw, contributors welcome! Know Python? If so, a very good way to jump into Swift programming is by contributing to Pythonic.swift: a Swift implementation of selected parts of Python standard library)
It was perfect for the Galaga-like level in my game. I only need to define a few control points to create a robust flight path for the enemy drones. The cool thing about the Catmull-Rom algorithm is that the spline passes through the control points.
Of course, you could do all of the above without SpriteKit. For example, for all of the rendering, you would simply write everything directly in OpenGL ES.
There are also cross-platform options, like Cocos2d-x  and Marmalade .
Finally, if you've read this far, you might be interested in reading my general thoughts and feelings from when I finished the game .