Pinta
Simple GTK# Paint Program
...Its goal is to provide users with a simple yet powerful way to draw and manipulate images on Linux, Mac, Windows, and BSD. Use easy drawing tools to draw freehand, lines, rectangles, ellipses, and more. Pinta includes over 35 adjustments and effects for tweaking your images. Use Pinta in your language. Pinta is at least partially translated into over 55 languages. Don't be afraid to experiment, Pinta tracks your full history so you can always undo. Use layers to help separate and group elements of your image for easy editing. ...