Artboard Studio - Online graphic design app mainly focused on product mockups.
Epic Pen - A windows tool for drawing over your desktop and applications
Vectr - Free vector graphics editor. A simple yet powerful web and desktop cross-platform tool for everyone.
gInk - An on-screen on-screen annotation software for Windows.
Canva - Canva is a graphic-design platform with a drag-and-drop interface to create print or visual content while providing templates, images, and fonts. Canva makes graphic design more straightforward and accessible regardless of skill level.
Ardesia - Ardesia is an usefull software for use your desktop as a Sketchpad.