I have an application that needs the user to enter the x and y location of a couple of items on the screen. [Yes, this is crap and I'll replace it, but for now...]

On Mac OS X, I'm using Snapz Pro X. When I choose to take a snap of a selection, the interface displays the mouse cursor location. This is OK for my personal use, but I can't ask users to buy a $69 program for this function.

I thought I had a solution with the built-in program "Grab", but it reports the coordinates from the bottom left, and I need it from the top left.

I don't have access to Windows; not sure what to use there. I've not even been able to come up with good search terms since mouse and coordinates and x/y are so common. Ideas are welcome there. Extra credit: same x/y finder for Linux. A Java program would be OK too, since the main application is in Java.