http://practicalswift.com/2014/06/27/a-minimal-webkit-browser-in-30-lines-of-swift/

webkitIn30lines.swift

#!/usr/bin/env xcrun swift

import WebKit

let application = NSApplication.sharedApplication()
application.setActivationPolicy(.Regular)

let window = NSWindow(contentRect: NSMakeRect(0, 0, 800, 600),
                      styleMask:   NSTitledWindowMask |
                                   NSClosableWindowMask |
                                   NSMiniaturizableWindowMask |
                                   NSResizableWindowMask,
    backing:     .Buffered,
    `defer`:     false)
window.center()
window.title = "Minimal Swift WebKit Browser"
window.makeKeyAndOrderFront(window)

class WindowDelegate: NSObject, NSWindowDelegate {
    func windowWillClose(notification: NSNotification) {
        NSApplication.sharedApplication().terminate(0)
    }

    func windowDidResize(notification: NSNotification) {
        print("windowDidResize called")
    }
}
let windowDelegate = WindowDelegate()
window.delegate = windowDelegate

class ApplicationDelegate: NSObject, NSApplicationDelegate {
    let _window: NSWindow
    init(window: NSWindow) {
        self._window = window
    }

    func applicationDidFinishLaunching(notification: NSNotification) {
        let webView = WebView(frame: self._window.contentView!.frame)
        self._window.contentView!.addSubview(webView)
        var urlString = Process.arguments.count > 1 ? Process.arguments[1] : "https://www.google.com/ncr"
        if false == urlString.hasPrefix("http://") && false == urlString.hasPrefix("https://") {
            urlString = "http://" + urlString
        }
        guard let url = NSURL(string: urlString) else {
            fatalError("Bad URL: \(urlString)")
        }
        webView.mainFrame.loadRequest(NSURLRequest(URL: url))
    }

    func applicationShouldTerminateAfterLastWindowClosed(sender: NSApplication) -> Bool {
        return true
    }
}

let applicationDelegate = ApplicationDelegate(window: window)
application.delegate = applicationDelegate
application.activateIgnoringOtherApps(true)
application.run()