The Spiro plugin can be used with AutoCAD to create Spirograph (TM)-like patterns. Turn your AutoCAD-based product into an educational toy that will provide hours of fun for the whole family!
This plugin was first published as an ADN Plugin of the Month: http://labs.autodesk.com/utilities/ADN_plugins. The plugin has been provided with the complete source code needed to build the application, with the intention of encouraging users of Autodesk software to use programming to tailor the products they use to their specific business needs.
More information regarding this plugin can also be found on Kean Walmsley's blog about AutoCAD programming, Through the Interface: http://blogs.autodesk.com/through-the-interface.