Mathematics:
Desmos is a free online graphing calculator that includes tutorials in how to use it. It seems like this might be interesting for a child who had a curious exploratory nature. They have 30 or so little lessons if you click to "open calculator" and then click on the three horizontal lines in the upper left hand corner. These lessons include "sliders" for certain variables so one can visualize how the line changes as one makes adjustments to the underlying formula.
Once a child has worked through the tutorials, they also have links from the home page (before "Open Calculator"). The "Staff Picks" links for math examples as well as art created through using equations, which should be intriguing.
