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.
RealWorld Paint - RealWorld Paint is an free portable image/photo/animation editor.
Autodesk SketchBook - SketchBook drawing and painting software provides designers, architects, and concept artists the tools to sketch ideas quickly and create beautiful illustrations.
miniPaint - Online graphics editing tool use HTML5 technologies like Canvas, Offline support, Drag and Drop.
Clip Studio Paint - The artist's software for drawing and painting.
JugiPaint - JugiPaint is a painting software with diverse tools for various types of illustration work.