This AutoHotkey script un-maximises the current active window (if it's maximized), resizes it to 1280x800 pixels and moves it to the center of a 1920x1080 screen, when WindowsKey+NumPad5 is pressed.
If you have a different screen resolution then you will have to modify the code. You can also update it to make it move to a diferent position or size, or change the hotkey.