Swift AppDelegate without Storyboard / XIB for iOS.

ACAppDelegate-macOS

@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {

    var window: NSWindow?

    func applicationDidFinishLaunching(_ aNotification: Notification) {
        // Insert code here to initialize your application
        mainWindowController = MainWindowController()
        mainWindowController?.showWindow(self)
    }
    
}

Application.swift

import Cocoa

class Application: NSApplication {

    let strongDelegate = AppDelegate()
    
    override init() {
        super.init()
        self.delegate = strongDelegate
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
}

Info.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	...
	<key>NSPrincipalClass</key>
	<string>$(PRODUCT_MODULE_NAME).Application</string>
  ...
</dict>
</plist>

MainWindowController.swift

import Cocoa

class MainWindowController: NSWindowController {
    
    init() {
        let window = NSWindow(contentViewController: MyViewController())
        super.init(window: window)
        window.title = "My Window Title"
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
}


class MyViewController: NSViewController {
    override func loadView() {
        self.view = NSView()
        self.view.frame = NSRect(x: 0, y: 0, width: 600, height: 400)
    }
}

Additional information can be found at https://stackoverflow.com/questions/40008141/nsapplicationdelegate-not-working-without-storyboard