Write to LanguageTool. They’re OSS in name only at the moment. I self-host their server, but the client is only usable on desktop and limited to web browsers without their paid version.
I’ve long been asking to be a customer, but to use their self-hosted server for privacy.
I think there’s a small but growing market for folks that want a quality grammar and spell check but don’t want data sent to the cloud.
If I could connect iOS to my LT server that’d be so rad.
Shawshank Redemption.
The Big Lebowski.
Also Star Trek 2.
So many great ones though.