Harper is a nice alternative, but it's still rough around the edges.

For instance, if you have a misspelled word, and the correction options come up, you can't get out of them and return to where you were by using the keyboard. You can hit Escape to close them, but it doesn't restore your place in the text field, so you have to use your mouse to get back where you were.

As a programmer who tries to use the keyboard as much as possible, this (incredibly easy to fix, I'm sure) bug drives me crazy! Almost enough to make me go back to Grammarly.