This is Unity Paint, a small painting application made with Unity 3D.
Unitypaint is a painting script to make it easier for game developers to paint on a texture.
up to 32x anti-aliasing
Check out the example web-player to see what you can do with it.
As of late 2011 the Unity Paint project may be used however you want, no restrictions. However a credit is always nice : D
Then it is just to download!