Krita - Krita is a professional FREE and open source painting program. It is made by artists that want to seaffordable art tools for everyone. Concept art. texture and matte painters, illustrations and comics.
Epic Pen - A windows tool for drawing over your desktop and applications
Artrage - A simple but lovely natural media painting and sketching program.
gInk - An on-screen on-screen annotation software for Windows.
PaintTool SAI - Learn to draw in different ways.
ZoomIt - Presentation utility for zooming and drawing on the screen.