Freeware
admaDIC Spiromat Applet
A Spiromat shows so called hypotrochoid curves. With the admaDIC Spiromat
you can display these figures. The inner ring can also be animated or controlled by
mouse so you can see how the figures emerge in detail.
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If you don't have a fast internet connection, you may wish to look at the Lo-Fi-Version which loads faster and uses smaller libraries.
Don't forget to take a look at the full featured admaDIC Spiromat Application which has many more features.