A clone of Apple's sample code game - DemoBot, which I've updated to compile with Swift 5.1 and Xcode 11.1. I tested the project on iOS 12.0 and macOS 10.15 (Catalina).
Please, take into account, do not switch off "Swift 3 @objc inference" in "Build settings" as Xcode recommends to you. After this project will not work properly.
Description by Apple:
DemoBots is a fully-featured 2D game built with SpriteKit and GameplayKit, and written in Swift. It demonstrates how to use agents, goals, and behaviors to drive the movement of characters in your game, and how to use rule systems and state machines to provide those characters with intelligent behavior. You'll see how to integrate on-demand resources into a game to optimize resource usage and reduce the time needed to download additional levels. DemoBots takes advantage of the Xcode scene and actions editor to create detailed levels and animations. The sample also contains assets tailored to ensure the best experience on every supported device.
For more information about DemoBots, see WWDC 2015 session 609, "Deeper into GameplayKit with DemoBots", available from https://developer.apple.com/videos/play/wwdc2015/609/.