iOS: Fleksy is an alternative keyboard with unprecedented predictive text skills. You can type a word absolutely incorrectly and it will still figure out what you meant.
That's because Fleksy was designed with the blind in mind. The keyboard not only fixes your typing errors, but speaks back the word to you so you know what it thinks you typed.
The keyboard only consists of letters. To make a space you swipe right. To delete a word you swipe left. You can add punctuation by pressing and holding the keyboard to reveal a new row, or you can just make two spaces to create a period, then swipe down to change it to a question mark, exclamation point, or something else.
While Fleksy takes a little getting used to at first, it's a very effective way to type because you can almost throw accuracy out the window. The only thing it does require is that you know how to spell, as it can't really figure out what you meant otherwwise. If you're vision-impaired or just an awful mobile typist but have good spelling skills, this is the keyboard for you. As an app it doesn't integrate full with the OS but you can use it to type out messages and copy/paste the text in elsewhere.
Fleksy (Free) [iTunes App Store]