I. Love. ArtRage. I’ve used natural-media drawing/painting tools for a loooong time, and have yet to find anything as fabulously great as ArtRage. The main thing it has going for it is simplicity; it takes about ten minutes of dicking around to figure everything out. As opposed to Painter, which has one of the densest, most incomprehensible interfaces I’ve ever seen. How on earth can artist-types figure it out?
ArtRage is a great example of a branded interface: distinctive, but doesn’t get too far in your way or require a lot of thinking to figure out controls. It lives in a single window and (almost) every control is replaced:

I’m generally not in favor of replicating system UI, but in this case, it works. I will say, however, that the modal dialogs, scrollbars or context menus are the weakest part of the interface. However, opting for consistency was probably the right choice.
On the plus side, the UI is clearly optimized for tablet input: The tool palette has big buttons, sliders both linear and circular are easy to manipulate with the more fluid, gestural input a stylus provides.
My very favorite bit, however, comes from an astoundingly clever bit of programming. The application uses PNGs as stencils, with black areas ending up knocked out and white as masked. To add to the library of stencils, all the user has to do is drop images into a directory, and they show up in the list. Not compiled in, not in some crazy database. Brilliant. Want to add a new section? Just add a directory; it’s name becomes the label. Don’t want to bother? There’s a GUI option to import stencil images into the individual file you’re working on. This is the best kind of extensibility: easy for the user who wants it, completely unnecessary and transparent to the user who doesn’t.
And the quality of the output? It’s certainly as close to real paint, pencil, marker and crayon as I’ve ever seen.
If you have a Wacom (does anyone else make them?) tablet, download it. If you don’t, buy a tablet, then download it. It’s one of the few truly pleasurable applications to use still around.

