From Harmony Hollow Software:
Use Screen Highlighter to annotate or highlight anything on your screen. Just have the program running and hit the hot-key combination whenever you need it. Draw freehand translucent lines around anything on your screen. Hold down Shift and move your mouse to draw translucent rectangles over anything on your screen. Hold down Ctrl and move your mouse to draw translucent ellipses. You can also use certain key and mouse-click combinations to stamp built-in icons like stars, checks, arrows, and more anywhere on your screen. Users can also specify options for line size and color and shape color. Handy for teaching or giving presentations.