Is it possible to reverse the screen, like in a mirror, with only 1 monitor?

On Windows, there are a few apps that can switch the graphics onscreen left to right (and vice versa), but to my knowledge, they all require at least 2 monitors. It seems like, because of the way Windows functions or by some mechanisms, the mirror transformation just can't work on a single screen. I wonder whether it's theoretically possible on Linux. Are there programs that do it already?