I recently built a small app that calculates a resistor's value based on color coding. This was an educational exercise in plain-vanilla javascript and old-fashioned html+css, although using jQuery would have saved me a lot of typing if nothing else. I tried to keep the color definitions and so forth as D.R.Y. as possible, going so far as to populate the select boxes from javascript using tedious DOM hacking. I'm sure many possible improvements will be immediately obvious to the attentive reader.