NSWindow without Storyboard - https://kicsipixel.github.io/2020/nostoryboard/

AppDelegate.swift

private var window: NSWindow?

func applicationDidFinishLaunching(_ aNotification: Notification) {
    
    let windowSize = NSSize(width: 480, height: 240)
    let screenSize = NSScreen.main?.frame.size ?? .zero
    let rect = NSMakeRect(screenSize.width/2 - windowSize.width/2, screenSize.height/2 - windowSize.height/2, windowSize.width, windowSize.height)
    window = NSWindow(contentRect: rect, styleMask: [.miniaturizable, .closable, .resizable, .titled], backing: .buffered, defer: false)
    window?.title = "No Storyboard Window"
    window?.makeKeyAndOrderFront(nil)
}

Final AppDelegate.swift

//
//  AppDelegate.swift
//  nostoryboard
//
//  Created by Szabolcs Toth on 11/01/2020.
//  Copyright © 2020 purzelbaum.hu. All rights reserved.
//

import Cocoa

// @NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {

    private var window: NSWindow?

    func applicationDidFinishLaunching(_ aNotification: Notification) {
         let windowSize = NSSize(width: 480, height: 240)
        let screenSize = NSScreen.main?.frame.size ?? .zero
        let rect = NSMakeRect(screenSize.width/2 - windowSize.width/2, screenSize.height/2 - windowSize.height/2, windowSize.width, windowSize.height)
        window = NSWindow(contentRect: rect, styleMask: [.miniaturizable, .closable, .resizable, .titled], backing: .buffered, defer: false)
        window?.title = "No Storyboard Window"
        window?.contentViewController = MyViewController()
        window?.makeKeyAndOrderFront(nil)
        
        // Get application name
       let bundleInfoDict: NSDictionary = Bundle.main.infoDictionary! as NSDictionary
       let appName = bundleInfoDict["CFBundleName"] as! String
     
       // Add menu
        let mainMenu = NSMenu()
        let mainMenuFileItem = NSMenuItem(title: "File", action:nil, keyEquivalent: "")
        let fileMenu = NSMenu(title: "File")
        fileMenu.addItem(withTitle: "About \(appName)", action: nil, keyEquivalent: "")
        fileMenu.addItem(NSMenuItem.separator())
        fileMenu.addItem(withTitle: "Hide \(appName)", action: #selector(NSApplication.hide(_:)), keyEquivalent: "")
        fileMenu.addItem(withTitle: "Hide Others", action: #selector(NSApplication.hideOtherApplications(_:)), keyEquivalent: "")
        fileMenu.addItem(withTitle: "Show All", action: #selector(NSApplication.unhideAllApplications(_:)), keyEquivalent: "")
        fileMenu.addItem(NSMenuItem.separator())
        fileMenu.addItem(withTitle: "Quit \(appName)", action: #selector(NSApplication.terminate(_:)), keyEquivalent: "q")

        mainMenuFileItem.submenu = fileMenu

        mainMenu.addItem(mainMenuFileItem)

        NSApp.mainMenu = mainMenu
    }

    func applicationWillTerminate(_ aNotification: Notification) {
        // Insert code here to tear down your application
    }


}

Final MyViewController.swift

//
//  MyViewController.swift
//  nostoryboard
//
//  Created by Szabolcs Toth on 11/01/2020.
//  Copyright © 2020 purzelbaum.hu. All rights reserved.
//

import Cocoa

class MyViewController: NSViewController {

    override func loadView() {
        let rect = NSRect(x: 0, y: 0, width: 480, height: 240)
        view = NSView(frame: rect)
        view.wantsLayer = true
        view.layer?.backgroundColor = NSColor.white.cgColor
        
        let label = NSTextField()
        label.frame = CGRect(x: view.bounds.width/2-50, y: view.bounds.height/2-22, width: 100, height: 44)
        label.stringValue = "Hello, World!"
        label.backgroundColor = .white
        label.isBezeled = false
        label.isEditable = false
        view.addSubview(label)
    }
}

Label.swift

let label = NSTextField()
label.frame = CGRect(x: view.bounds.width/2-50, y: view.bounds.height/2-22, width: 100, height: 44)
label.stringValue = "Hello, World!"
label.backgroundColor = .white
label.isBezeled = false
label.isEditable = false
view.addSubview(label)

main.swift

import Cocoa

let delegate = AppDelegate()
NSApplication.shared.delegate = delegate
_ = NSApplicationMain(CommandLine.argc, CommandLine.unsafeArgv)

Menu.swift

// Get application name
let bundleInfoDict: NSDictionary = Bundle.main.infoDictionary! as NSDictionary
let appName = bundleInfoDict["CFBundleName"] as! String

// Add menu
let mainMenu = NSMenu()
let mainMenuFileItem = NSMenuItem(title: "File", action:nil, keyEquivalent: "")
let fileMenu = NSMenu(title: "File")
fileMenu.addItem(withTitle: "About \(appName)", action: nil, keyEquivalent: "")
fileMenu.addItem(NSMenuItem.separator())
fileMenu.addItem(withTitle: "Hide \(appName)", action: #selector(NSApplication.hide(_:)), keyEquivalent: "")
fileMenu.addItem(withTitle: "Hide Others", action: #selector(NSApplication.hideOtherApplications(_:)), keyEquivalent: "")
fileMenu.addItem(withTitle: "Show All", action: #selector(NSApplication.unhideAllApplications(_:)), keyEquivalent: "")
fileMenu.addItem(NSMenuItem.separator())
fileMenu.addItem(withTitle: "Quit \(appName)", action: #selector(NSApplication.terminate(_:)), keyEquivalent: "q")

mainMenuFileItem.submenu = fileMenu

mainMenu.addItem(mainMenuFileItem)

NSApp.mainMenu = mainMenu

MyViewController.swift

 override func loadView() {
    let rect = NSRect(x: 0, y: 0, width: 480, height: 240)
    view = NSView(frame: rect)
    view.wantsLayer = true
    view.layer?.backgroundColor = NSColor.white.cgColor
 }