programmatically create initial window of cocoa app (OS X)

See https://github.com/sindresorhus/touch-bar-simulator/blob/master/Touch%20Bar%20Simulator/main.swift

In main.swift

let app = NSApplication.shared()
let delegate = AppDelegate()
app.delegate = delegate
app.run()

Swift 4:

// File main.swift
autoreleasepool {
   // Even if we loading application manually we need to setup `Info.plist` key:
   // <key>NSPrincipalClass</key>
   // <string>NSApplication</string>
   // Otherwise Application will be loaded in `low resolution` mode.
   let app = Application.shared
   app.setActivationPolicy(.regular)
   app.run()
}

// File Application.swift
public class Application: NSApplication {

   private lazy var mainWindowController = MainWindowController()
   private lazy var mainAppMenu = MainMenu()

   override init() {
      super.init()
      delegate = self
      mainMenu = mainAppMenu
   }

   public required init?(coder: NSCoder) {
      super.init(coder: coder) // This will newer called.
   }

}

extension Application: NSApplicationDelegate {

   public func applicationDidFinishLaunching(_ aNotification: Notification) {
      mainWindowController.showWindow(nil)
   }
}

I spent an entire Sunday digging into this problem myself. Like the person asking the question, I prefer coding iOS and OSX without nib files (mostly) or Interface Builder and to go bare metal. I DO use NSConstraints though. It is probably NOT WORTH avoiding IB if you're doing simpler UIs, however when you get into a more complex UI it gets harder.

It turns out to be fairly simple to do, and for the benefit of the "Community" I thought I'd post a concise up to date answer here. There ARE some older Blog Posts out there and the one I found most useful were the ones from Lap Cat Software. 'Tip O The Hat' to you sir!

This Assumes ARC. Modify your main() to look something like this:

#import <Cocoa/Cocoa.h>
#import "AppDelegate.h"

int main(int argc, const char *argv[])
{
    NSArray *tl;
    NSApplication *application = [NSApplication sharedApplication];
    [[NSBundle mainBundle] loadNibNamed:@"MainMenu" owner:application topLevelObjects:&tl];

    AppDelegate *applicationDelegate = [[AppDelegate alloc] init];      // Instantiate App  delegate
    [application setDelegate:applicationDelegate];                      // Assign delegate to the NSApplication
    [application run];                                                  // Call the Apps Run method

    return 0;       // App Never gets here.
}

You'll note that there is still a Nib (xib) in there. This is for the main menu only. As it turns out even today (2014) apparently no way to easily set the position 0 menu item. That's the one with the title = to your App name. You can set everything to the right of it using [NSApplication setMainMenu] but not that one. So I opted to keep the MainMenu Nib created by Xcode in new projects, and strip it down to just the position 0 item. I think that is a fair compromise and something I can live with. One brief plug for UI Sanity... when you're creating Menus please follow the same basic pattern as other Mac OSX Apps.

Next modify the AppDelegate to look something like this:

-(id)init
{
    if(self = [super init]) {
        NSRect contentSize = NSMakeRect(500.0, 500.0, 1000.0, 1000.0);
        NSUInteger windowStyleMask = NSTitledWindowMask | NSResizableWindowMask | NSClosableWindowMask | NSMiniaturizableWindowMask;
        window = [[NSWindow alloc] initWithContentRect:contentSize styleMask:windowStyleMask backing:NSBackingStoreBuffered defer:YES];
        window.backgroundColor = [NSColor whiteColor];
        window.title = @"MyBareMetalApp";

        // Setup Preference Menu Action/Target on MainMenu
        NSMenu *mm = [NSApp mainMenu];
        NSMenuItem *myBareMetalAppItem = [mm itemAtIndex:0];
        NSMenu *subMenu = [myBareMetalAppItem submenu];
        NSMenuItem *prefMenu = [subMenu itemWithTag:100];
        prefMenu.target = self;
        prefMenu.action = @selector(showPreferencesMenu:);

        // Create a view
        view = [[NSTabView alloc] initWithFrame:CGRectMake(0, 0, 700, 700)];
    }
    return self;
 }

 -(IBAction)showPreferencesMenu:(id)sender
 {
    [NSApp runModalForWindow:[[PreferencesWindow alloc] initWithAppFrame:window.frame]];
 }

-(void)applicationWillFinishLaunching:(NSNotification *)notification
{
    [window setContentView:view];           // Hook the view up to the window
}

-(void)applicationDidFinishLaunching:(NSNotification *)notification
{
    [window makeKeyAndOrderFront:self];     // Show the window
} 

And Bingo... you're good to go! You can start working from there in the AppDelegate pretty much like you're familiar with. Hope that helps!

UPDATE: I don't create menus in code anymore as I've shown above. I've discovered you can edit MainMenu.xib source in Xcode 6.1. Works nice, very flexible and all it takes is a little experimentation to see how it works. Faster than messing around in code and easy to localize! See the picture to understand what I am on about: