[T]his I/O Brush lets you take textures, colors, and even movements found in the world and use it to paint. Sound confusing? Well, textures and colors are pretty straightforward. You take the brush and point it at say, a watermelon, and when you paint with the brush the watermelon texture is your brush-stroke.
Not clear? A picture is worth a thousand words. Check it out here.
Read more about it here.
Hat tip, Peter at alarm-alarm.