TwistedBrush Pro Studio - A powerful and unique natural media painting program.
Krita - Krita is a professional FREE and open source painting program. It is made by artists that want to seaffordable art tools for everyone. Concept art. texture and matte painters, illustrations and comics.
Corel Painter - Corel Painter is media painting software.
Artrage - A simple but lovely natural media painting and sketching program.
MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.
Clip Studio Paint - The artist's software for drawing and painting.