The Apps I found (the orange highlighted are my favorite ones):
- Notes on iPhone — probably the simplest sketch tool you can find on a phone
- Drawing Desk — different pen tools, layers
- Concepts — pen tools, layers
- Bloom — More like a coloring book
- Lake — can put colors on other people’s sketches
- Sketchbook — As the name indicates, different pen tools, color options.
- 风景与艺术(Scenery & Art) — does not really allow you directly draw anything but provides a cool assets of historical painting elements. Allow the user to pick up different components to put directly onto the canvas. Also has an encyclopaedia function (if you click on the elements you put, it shows the history of that specific element)
- Paper — like it because of the sketch book design of it.
- Sketches —really nice pen tools and lovely ui design (also have layers but need to pay for it)
- 画吧（Hua Ba [just draw it]) — nice interface design and color options