I have been working on an android app that allows you to control Ryan’s CNC router (“Goliath”) directly via touch. After a few iterations, I’ve got an app that I’m quite happy with. It supports circles, rectangles, lines as well as freehand. The app also lets you specify your cut area and cut depth on the fly (check out Tic Tac Toe take 2 for a good example of why defining cut area on the fly is useful). Check out the forum thread that describes the app in more detail.
Here are some demo videos of the app in action:
Smiley face demo (full demo of all features)
Tic Tac Toe, take 1 (first trial)
Tic Tac Toe, take 2 (continuation of first trial)
Thanks to Ryan for designing such an incredible machine and to Albert for filming/editing.