I found this to be a useful idea for me when highlighting lines of code that stretch further than the a screens horizontal bounds. Maybe looking at turning this into a complete mouse/keyboard utility. But for now it does just that. Locks the mouse coordinates.
No screenshot, sorry. But not much to really show, has a notify icon (w/ menu) and a basic form with 2 check boxes. For the lock to engage, press down and hold the space bar.