0.md

1. Build app like this
2. Open app
3. open omgscheme://whatever

Info.plist

  <!-- ... -->
	<key>CFBundleURLTypes</key>
	<array>
		<dict>
			<key>CFBundleURLName</key>
			<string>Whatever!</string>
			<key>CFBundleURLSchemes</key>
			<array>
				<string>omgscheme</string>
			</array>
		</dict>
	</array>
  <!-- ... -->

main.swift

import Cocoa

class AppController: NSObject, NSApplicationDelegate {
    let openerPath = "/idk/wherever/you/want"

    func applicationWillFinishLaunching(aNotification: NSNotification) {
        NSAppleEventManager.sharedAppleEventManager().setEventHandler(
            self,
            andSelector: #selector(AppController.handleGetURLEvent(_:withReplyEvent:)),
            forEventClass: AEEventClass(kInternetEventClass),
            andEventID: AEEventID(kAEGetURL)
        )
    }

    func handleGetURLEvent(event: NSAppleEventDescriptor?, withReplyEvent: NSAppleEventDescriptor?) {
        defer { NSApp.terminate(self) }

        if let event = event {
            let url = event.paramDescriptorForKeyword(AEKeyword(keyDirectObject))!.stringValue!
            let task = NSTask()
            task.launchPath = openerPath
            task.arguments = [String](arrayLiteral: url)
            task.launch()
            task.waitUntilExit()
        }
    }
}

let app = NSApplication.sharedApplication()
let con = AppController()
app.delegate = con
app.run()