Run by a team that dubs themselves Colorjack, this "Sketchpad" demo shows off the capabilities of modern JavaScript and HTML5 support. You can paint any color in any shade or opacity, take on patterns and "Spirographs," and use all the tools you're likely familiar with from Microsoft's older versions of that old Paint standby.
Sketchpad also offers a handful of control windows you can move around and keep open. If the app supported drag-and-drop file imports, as Firefox 3.6 does, this would be a truly robust, and almost desktop-replacing, webapp.
When you're done with your efforts, hit the save icon and your image pops up in a new tab, ready to be saved. Sketchpad is free to use, and works on any browser that supports HTML5—including, it's been suggested, in some mobile devices, though we had very little luck actually painting with an iPod touch and Android device.
