The very talented Ben Gotow has just released a brand new iPhone app called Layers, his third now after Mathomatic and NetSketch (iTunes links). Layers, not to be confused with the innovative screen capture application on the Mac desktop, is a natural media painting app for the iPhone. Stating the obvious, it incorporates Photoshop-like layers, as well as a variety of brush and color selection options, panning, zooming and the ability to export your masterpieces as JPG or Photoshop PSD files (layers included).
I gave it a run-through and am extremely impressed with the implementation. I am no painter, a fact hinted at by my not posting any screenshots of my own work. However, I'm adept enough with digital art to recognize that this is a very intuitive interface. Manipulating layers is done in a side view with layer previews, allowing a tap-and-drag re-ordering and one-tap addition and subtraction of layers. I especially appreciate the 30 levels of undo history, making it simple to backtrack errant swipes. The application allows for sophisticated artistic expression beyond mere "finger painting," and, with a little practice, you can create some complex imagery. The layering functionality even allows for photo compositing, using multiple layers with photos and the eraser tool to remove portions of the top layers. This is more in line with my personal skill set, so I had some fun with this. Tight erasing can be a little tricky when you have big fingers which are hard to see around, but the undo functionality and some dedication make it perfectly feasible.