Illus is a minimal drawing program based on Python and Tkinter.
Madeline 2.0 Pedigree Drawing Engine (PDE)
A drawer for origami crease pattern
Paint brush program which you can draw objects, Object Painter
Pencil2D is a cross-platform animation/drawing application.
Simple drawing program for Linux
Simple and basic whiteboard drawing app in html5.
A canvas you can draw on with different colors
2D CAD for precise drawing