One thing that was the "killer app" for graphing calculators, at least through college in the last decade (even with wifi), was the fact that there were apps.

One thing that was the "killer app" for graphing calculators, at least through college in the last decade (even with wifi), was the fact that there were apps. Graphing calculators were the first mass market mobile computers under $200 with what you could almost refer to as an app store, via ticalc.org (oh how many hours I spent on there). The interfaces had to be easy to use with low resolution screens and usually four directional buttons. Apps had to be about content. Games were pretty fun. My TI-89 has survived 11 years. It's survived bike falls, being thrown across the room several times (when I was too quick to grab it and it went flying out of the cover). I use it infrequently but the batteries haven't been changed in over a year. I still have more screen real estate when I am typing on it than I do with my iPhone 5 (both in vertical and landscape). It has actual buttons and I have muscle memory so I don't even have to look at it when I type in numbers and symbols. I have a periodic table app on my TI-89 that has been on there since 2003. The information someone in chemistry or physics needs is quicker to access than http://www.ptable.com http://www.ptable.com or wikipedia. I'm sure there are apps on an iPod that are probably better now, but an iPod's batteries don't last months. What could usurp it? Something in the same form factor that can last 48+ hours and take AA or AAA batteries. Something that provides temporary instructor override, allowing an instructor to enforce a policy temporarily (i.e. disable the CAS). Something that might integrate well with tools from TI that are out there. Something that's useful from middle school up to engineering/chemistry/physics. Maybe something e-ink (and/or e-ink buttons), plastic, ARM or Atmel, Linux, python and some sort of CAS (Mathematica/Maple branded) by default, with an App store/ecosystem. Something $50-$75. WiFi only, but off by default. Something that probably looks a bit like a nokia n800 or blackberry. I think that would be reasonable.