Concepts - Concepts is a digital design sketchbook for iPhone, iPad, iPad Pro and windows 10 devices.
Crystal: Sketch Mirror for Android - Crystal: Sketch Mirror for Android is an application that is designed for viewing your sketch designs in real-time, navigate prototypes and download content related to the sketches for offline viewing.
Collect by WeTransfer - Collect by WeTransfer is the best way to organize your ideas.
Figma Mirror - Figma Mirror is an application that covers top trending designing or sketching ideas making your teamwork in a single environment and design better products from start to finish.
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.
Flowkit - Sketch library for user flows/content maps/annotations