Preferences

Use an NSPanel for the window.

To make the window title match the selected tab (as per the HIG), there's a sentence in the contentViewController documentation that tells you how to make it work. In Swift, it's:

window!.bind(.title, to: contentViewController!, withKeyPath: "title", options: nil)

or you can edit the Window Controller bindings in IB, to bind the Title to self.window.contentViewController.title.