Well, part of the reason why TI hardware is required and not just graphing software is that students often need something they can take home with them. Laptops

Well, part of the reason why TI hardware is required and not just graphing software is that students often need something they can take home with them. Laptops running GNU/Linux, despite having no software costs, will still be significantly more expensive than even $140 calculators. What is needed is an open source, cheap hardware calculator, and as far as I know, nobody has anything like that on the market.