A site dedicated to "art, research and play in creative interaction design using sound, physical and virtual space," squidsoup.org offers some interesting interactive projects to peruse.

One of the projects which allows online play is Doodle . You're given the opportunity to draw a shape with your mouse (hold the left mouse button down, and drag it across the field to create spirals and other shapes), you can then view the shape as it begins to turn and twist in a virtual 3D way.

I minimized the window and continued to do other things before coming back to my original doodle, and found that it had grown and changed, sprouting long arms that added more and more depth to the "doodle". The closer I moved my cursor to the center of the object, the more slowly it turned. The further away my cursor was from the center, the faster it turned.

The idea behind it is to explore direct drawing in 3D space; I happen to find the technology behind it fascinating.