This is drawthings. It lets you sketch really quickly. You choose white-on-black or black-on-white. You also get red.
It's great like a piece of paper is great. UX prototypes. Quick charts and graphs. Your daughter's first masterpiece.
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* QUICK NOTE: A couple of people have had an issue with the app not starting properly when first downloading it from the App Store. This is a download corruption issue from Apple, and has a quick fix: just remove and redownload the app. Happy sketching!