Doom The Way it Was Meant to Be Played - v1.1 Multi-monitor

Yes. Well, sort of.

Different types of graphics cards would map themselves to different areas of memory, so it was possible to have more than one graphics card so long as the memory used by the graphics cards didn't overlap. Generally, this meant one of the cards was monochrome and the other could be something like VGA. DOS itself had no idea what to do with more than one graphics card. However, both graphics cards were mapped to to the processor's address space and DOS had no memory protection so applications had full access to the hardware and could talk directly and utilize both graphics cards.

The way I saw it used was with a very old computer controlled microscope. The monochrome card/monitor was actually the main screen that the computer booted up with (which was kind of funny with a 486), and this is where you controlled the microscope in their application. The VGA card was the secondary that was used to display images.

I read that it was written with multiple concurrent views but I can't remember why. Carmack, anyway.