A little over a year ago, developer Doug Melton delighted us with Android emulators for three popular TI calculators - TI-83, TI-85, and TI-86. Nostalgic and surprisingly useful, they resonated with many of you, but, unfortunately, TI forced Doug to take them all down a short while after.
You see, Doug actually shipped them with the original ROMs included, which was great for one-click installations, but apparently not so great for intellectual property. Oh, and he did name them TI-83, TI-85, and TI-86 originally, giving Texas Instruments an even simpler reason to have the apps removed.
In addition to all of the above, TI-89, the king among TI calculators and one of my personal favorites, has never (to my knowledge) existed on Android.