I'm not 100% sure what the real uses for this would be, but a nice generic solution would be a program with 2 "regions", or rather a window and a region selector. The window could be placed and sized as desired, and would display the contents of the selected region, which could be moved anywhere.
So basically this is like a "magnification" tool, except that it can before enlargement or reduction, and doesn't follow the cursor, but rather shows the content of a selected region on your screens.
I wouldn't be surprised if such a program didn't already exist.. if someone finds it (or writes it!) please post.
Could be useful for given presentation talks, etc.
Giving presentations is exactly what this would be used for. I give a lot of them and currently I have to look at the screen where the presentation display is being projected to see what I am typing. It would be so much faster and convenient if I was able to see what I was typing in a simple window on my main display.