1024-level touch-sensitive canvas. You can use a brush on it. It's also an LCD screen. To use a brush you pick a color using another digital display. Can use various color models and an artist's palette where you mix colors using the brush.
The good thing about *this* canvas is that it has an undo.
Other possible options: Apply certain filters to the image or change its colors, use brush modes available in Photoshop, vector graphics module
Automatically save work every few seconds or as close to real-time as possible.
Can transfer paintings to computer via USB.