How to Move an Off-Screen Window Back On-Screen on macOS

If you're seeing that error message on a black background in white letters, it means that your Mac is stuck trying to boot into BootCamp, but there's nothing to boot, since you've just removed Windows. What you need to do, is to tell your Mac to boot back into OS X. Try this:

1. Power down your Mac and make sure it's turned off.
2. Turn it back on, and when you hear the startup sound, hold down and Option (Alt) key on the keyboard.
3. If you did everything correctly, you should see a list of disks you can boot from, including Macintosh HD (or whatever it's called if you renamed it in the past).
4. When you're back in Mac OS X, fire up System Preferences and click the Startup disk control panel icon. Make sure that your Macintosh HD disk is selected as the default boot disk.
5. Finally fire up BootCamp Assistant to completely remove all traces of the Windows partition off your hard drive. If you're brave and are sure what you're doing, you can also use Disk Utility for that, but be careful, it's not as straighforward to use as Bootcamp Assistant.

I hope this helps!

Doesn't exists. If you want this feature you have to use an external program. For such thing, I use Moom (10$) where you can define a shortcut for it. Checkout the screenshot:

This let me use ⌥alt+⇥tab to move the active window to the desktop on the right.