This is yet another idea that came to me while playing with
my kids: create a Coloring book activity.
I would need to try and find some attractive black&white
drawings. The UI would consist of this drawing and a color palette
at the side (or bottom). Choose a color, click a white spot,
the spot is filled with that color (paint bucket).
Choose another color, click in the colored spot again, and you
get a gradient fill...
I am not yet sure what the best technology is for implementing
this. I think about looking into the SVG coloring code in python