Forge is a complete design studio wrapped in a very well considered and constructed app. It is an absolute pleasure to use.
The app organises sketches into projects, and allows individual sketches to be duplicated to try out different colour schemes and whatnot- their built in example of a scooter design is very helpful.
You get a range of variable tip width tools, including a chisel tip that actually behaves as you'd expect.
There are a range of well matched palettes and of course you can create your own.
There are 4 layers that can each have their opacity set, pinch to zoom, and sadly two finger swipe to undo... which does work,and didn't do too many false strokes.
Export to all number of places- the only wrinkle being that if you export as a png, you'll need to stick in a plain coloured background layer as it creates a transparent png.