And I don't mean some obnoxiously advertised chrome plugin but a core part of spell check on my devices.
Also while I'm here: ios autocomplete is infuriating. It's constantly learning complete jibberish typo words and so I have to reset it every few months.
I'm a little ashamed to admit this, but the feather on the camel's back was a word I commonly use autocorrecting to 'ducking'. Infuriating. I remember listing to a podcast with Ken Kocienda - former iOS engineer who wrote the original iPhone keyboard with the dictionary; it was intentional.
I like it when it truly catches a real mistake but grammar is more flexible than it believes it is.