When Hoplite Industries needed some overpriced spacers, I was able to 3D print some suitable alternatives for a fraction of the cost using OpenJSCAD! Watch my talk at Big Sky Dev Con in which I talk about making real things using code.
O'Reilly Media's Oriole platform provides a rich learning experience by combining video, text and interactive coding widgets. To me, it seemed like the perfect way to teach Arduino, but interfacing with Arduino from a browser is tricky business. Read about how I managed to get a simple example going that includes writing code, uploading it to your Arduino and using your Arduino to interact with widgets on the page, all from your browser window.