Invision - Prototyping and collaboration for design teams
Microsoft Paint - Paint (formerly Paintbrush) is a simple, ultra-basic graphics painting program that is included...
Proto.io - Create fully-interactive high-fidelity prototypes in minutes that look and work exactly like your app should. Sign up for a free 15-day trial and get started.
MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.
Zeplin - Collaboration app for UI designers & frontend developers
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.