From Sean J MacIsaac:
MyPaint is a fast and easy open-source graphics application for digital painters. It lets you focus on the art instead of the program. You work on your canvas with minimum distractions, bringing up the interface only when you need it. MyPaint comes with a large brush collection including charcoal and ink to emulate real media, but the highly configurable brush engine allows you to experiment with your own brushes and with not-quite-natural painting.
What's new in this version:
Version 1.0 includes configurable toolbar has been added with dropdown widgets for color, brush, and brush settings, floating tool windows can now be docked into a sidebar inside the main window, and Mouse and stylus buttons can be bound to different actions via the preferences.