Epic Pen - A windows tool for drawing over your desktop and applications
Gromit-MPX - Create annotations by directly drawing on your screen.
gInk - An on-screen on-screen annotation software for Windows.
Ardesia - Ardesia is an usefull software for use your desktop as a Sketchpad.
ZoomIt - Presentation utility for zooming and drawing on the screen.
Pylote - To draw on the screen and to handle the instruments of geometry there.