MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.
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.
Autodesk SketchBook - SketchBook drawing and painting software provides designers, architects, and concept artists the tools to sketch ideas quickly and create beautiful illustrations.
Paint.NET - Paint.NET is a free image and photo editing software.
Clip Studio Paint - The artist's software for drawing and painting.
PaintTool SAI - Learn to draw in different ways.