A couple of months ago, I spent a few weeks playing with <canvas>. The main reason was to write a game (currently on the back burner, but not "cold" as yet), and also to re-learn some simple mechanics and trigonometry I've forgotten since c.1993. I've put together a little bit of code ("testbed") which lets me put together simple interactive diagrams. Due to the lack of text support in <canvas>, unfortunately I can't label everything diligently. My old maths teacher, Mr. Slatter, would be horrified.