Crafting new instructional aids for math courses can be difficult, but this helpful new article from Markus Hohenwarter and Judith Preiner will bring much joy to the hearts of mathematics teachers everywhere. This particular article presents information on creating new interactive materials (or "mathlets") with the use of various open source tools. The article includes sections on creating mathlets for discussing tangents to a circle, slope functions, and even offers up some suggestions for creating dynamic worksheets. The piece also describes how to crate interactive exercises with JavaScript and it concludes with a set of additional reference materials and resources.