Harmen Zijp (one of the main Spullenmannen) created the Parametric SVG editor. It's a tool that enables you to create/load svg (vector) drawings and make parts of them dynamic. This means that by changing a parameter you can easilly change the whole design. In the screenshot above you see a foldable box which has a dynamic width, height and depth.
In return for a trip to Norway I helped him take this handy tool to the next level. I added crossbrowser compatibility, corrent handling of size units, foldable menu items, duplication, selection boundingboxes, a better shared designs overiew, adding elements shortcuts, a macro button and a slight redesign.