MyPaint is free open-source graphics application for digital painters. It lets you focus on the art instead of the program.It comes with a large brush collection including charcoal and ink to emulate real media.
Main features:
Available for Windows and GNU/Linux
Designed for pressure sensitive graphics tablets
Simple and minimalistic user interface
Extensive brush creation and configuration options
Unlimited canvas (you never have to resize)
Basic layer support
Download MyPaint