I just ran across Language Tool[0] recently. Free, open-source proofreading lib, can be run totally locally. Uses Google Ngrams to check for often confused words. Didn't correct "doe snot" in my synthetic test just now, but that seems like a plausibly minor extension of existing functionality.

[0] https://www.languagetool.org/

There’s at least one product trying to address the issue with “valid, but probably wrong” typos. It’s called Grammarly and for some unfathomable reason it gets advertised to me a lot on YouTube whenever Google detects I’m in South Korea; I believe they are seriously mistargeting their marketing efforts.

(That said, if it were me, I’m not sure if I would give up typing doe snot every once in a while.)

Defiantly.

The spell checker in Chrome can already do that to some extent. For example, "The men walked over their to grab they're food." gets corrected: https://i.imgur.com/NR4zyVA.png

command-not-found [1] could implement that, if it isn't implemented already. I remember a Linux distribution with an application which would let a train pass in a few seconds after typing typical commands wrong. Trust me, you'll learn to type correct when that happens because it is very annoying.

EDIT: as mentioned below, it is called 'sl'

[1] https://wiki.ubuntu.com/CommandNotFoundMagic

The spelling checker in Word has some grammar rules, try to configure those if she uses Word.

defintitely