The only thing that immediately comes to mind when reading through the chapter, especially the sections on determining position and event listening is this old website I stumbled upon years ago that tracked your mouse across the screen. The fun part about the site is that no matter where you moved the mouse, it would come up with a photo of someone pointing to your exact location on the screen. The number of photos that they included was crazy! I'd post the link here, but unfortunately, I lost track of it a while back and haven't been able to track it down again.
I mean, it doesn't have to be limited to simply making a grocery list, it could be used for making regular lists or even just taking notes. Other than that, I'm drawing an absolute blank at the moment. Apologies!