I would have paid for this when I was in high school. Maybe up to $15 or $20/month. When I found Maple in university and the step-by-step demonstrations of inte

I would have paid for this when I was in high school. Maybe up to $15 or $20/month. When I found Maple in university and the step-by-step demonstrations of integration and derivatives, it was a godsend. I could pinpoint the exact step I didn't understand and work from there. Consider targeting specific standardized tests. Parents seem to pay good money for their kids to have an advantage on standardized tests. As far as prototyping, it could be a matter of taking something like Sage, Maxima, or Eigenmath and adding some hooks to output intermediate steps and text helper messages. They all output LaTeX IIRC, so you just need to hook that up to a latex-to-png program to render. You can target a specific problem like derivatives or simple integrals, and run some adwords for it to see if there is any interest.