Open Peeps - A hand-drawn illustration library.
Artrage - A simple but lovely natural media painting and sketching program.
Control Illustrations - 108 free flat illustrations with customizable characters
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.
DrawKit - MIT licensed SVG illustrations, in 2 styles
Clip Studio Paint - The artist's software for drawing and painting.