MathCoder allows you to encode short messages using simple addition and subtraction problems. I created MathCoder as a drill for my first grader, who needed to practice his addition and subtraction.
I had attempted a jigsaw puzzle creator too, with mixed success. It’s a bit temperamental…it works on a JPG image that you upload and superimposes jigsaw puzzle outlines on the image. The output is a PDF document that contains both a reduced resolution image of the original picture with the jigsaw outlines, as well as additional pages with four puzzle pieces per page. Unfortunately, to complete the puzzle, you would need to snip each puzzle piece out with a pair of scissors…Perhaps there is a laser engraver in my future?