IOS
Voice Control on iPhone and iPad
Not Siri, and far more useful for anyone who cannot rely on touch. Voice Control replaces the finger entirely: you say "tap", "swipe" or "type" and the phone does it. When you cannot name a button, saying "show numbers" tags every item on screen, and "show grid" lays a numbered grid over the rest.
Once its language files have downloaded it no longer needs Wi-Fi, which is the difference between a feature that works in a hospital parking lot and one that sulks without a signal. It costs nothing on a device you may already own, so try it for a week before spending money on anything else on this list.
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