Windows/Mac/Linux: IOGraph is a free utility that tracks your mouse movements to create surprisingly beautiful works of computer art.
(Click the image above for a closer look.)
The app works simply: Download it, run it and hit the big record button to get started. Just let it run while you work, check in occasionally to see how your work of art is coming along, and when you like where you're at, just click the Save image button.
IOGraph is a free download for Windows, Mac and Linux. If you give it a try, share your results in the comments.