Mr. Draw is an open-source Game Maker paint program. It has quite a bit of features, all of which can be found here:

    * Drawing without spaces
    * Magnifying
    * Changing line width (line size)
    * Custom Colors
    * Supports saving pictures as .gif,.png.,bmp, and .jpg
    * Supports changes in size of picture (to a maximum of 600 width and 400 height)
    * Saving as .pod for future use of project (or to keep working on your project)
    * Random Colorizing
    * Grayscale effect
    * Custom Colors
    * Various Tools (pencil, eraser, color changer, magnifier, eyedropper)
    * Smooth magnifying movement
    * Smooth erasing
    * Line tool
    * Rectangle tool

Quickplay to see the executable, download for executable and .GMK source.