Back in the Android 2.0 days, a guy had a set of TI emulators which, when loaded with the ROM downloadable directly off of TI's website, perfectly replicated several well-known TI calculator models. Think the one I used got shut down, but there's a number of newer ones:
https://play.google.com/store/apps/details?id=com.Bisha.TI89...
I already owned a TI calculator at the time, it was just nice not to carry it around. TI probably would still make good money selling an official version.