Desk Marker

I’ve found a pretty nifty (and free) program on the Internet called Desk Marker.

Basically it will allow you to turn your mouse into a desktop drawing tool so that you can annotate what is on the screen. What is even more useful is that when you move any windows around the screen after you have drawn your doodles, the markup will remain as long as it’s visible.

The only catch is that the inteface is a little clunky (you have to press and hold ALT+1 to use the pen by default).