The sketchbook app is a great tool for drawing and sketching out ideas. I would give it a 4 of 5 for apps because it can be used on iPhone or iPad. But I think it will be cool if you can use it on a computer monitor as well.
It’s a free app and service artists and designers can use. At Autodesk, we believe creativity starts with an idea. From quick conceptual sketches to fully finished artwork, sketching is at the heart of the creative process. You never know when a great idea will strike, so access to fast and powerful creative sketching tools is an invaluable part of any creative process. (https://sketchbook.com)