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.

WWW: http://mypaint.intilinux.com/
