How to support multiple screens?

How can I support multiple screens in Unity? For example, a pretty common configuration is a laptop with an external monitor plugged in. Suppose we want to show (say) the instrument console on the laptop screen, and the view out the window on the external screen. How can we do it?

OK, yes, I realize I could launch a second app, and have the two apps communicate through a local socket or some such. But... ouch. Is there any other way to do it? Within a single Unity app?

Thanks,
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How to support multiple screens?