A simple, but still feature-rich, graphic editor
A dithering software based around floats
Grab screen areas and note it with a mouse, pen & keyboad quickly.
Paint brush program which you can draw objects, Object Painter
Multi-Monitor Wallpaper Editor
Advanced image processing toolbox for Scilab on Unix/Linux/Mac OS
Image editor / converter for MCU-based embedded projects
Simple drawing program for Linux
A cross-platform C64 hires bitmap editor...