Epic Pen - A windows tool for drawing over your desktop and applications
Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
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.
Sketch - Professional digital design for Mac.
PaintTool SAI - Learn to draw in different ways.
Affinity Designer - Professional creative software, exclusively for Mac.