I recently stumbled across Charcoal on iOS when looking for a simple sketch/drawing app for quickly visualising something. Sometimes you don't need all the bells and whistles of something like Procreate, and Charcoal fits the bill perfectly for what I needed at the time. In my limited testing on my iPad (with and without a Pencil) it's been fast, responsive, accurate, and intuitive.
One (odd) thing I was very impressed by is the size of the app bundle – it's tiny, at less than 700KB!
