Open Peeps - A hand-drawn illustration library.
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.
Control Illustrations - 108 free flat illustrations with customizable characters
Procreate - Procreate is the most powerful and intuitive digital illustration App available for iPad®.
Craftwork - A collection of User Interface resources made by Craftwork
Autodesk SketchBook - SketchBook drawing and painting software provides designers, architects, and concept artists the tools to sketch ideas quickly and create beautiful illustrations.