I use MessagEase, which has a wacky layout that makes typos much less frequent, and thus doesn't need autocorrect. Not open-source, unfortunately.
Oof. Just looked it up and it immediately gets my fancy. How was the learning curve? And any downsides that you now have?
The lack of autocorrect was so refreshing that I just kept typing for practice.
The downside now is that, unlike the QWERTY to Dvorak switch, I've become exceedingly clumsy at typing on ordinary phone keyboards.