https://gradeproof.com is a direct competitor with some great tools. I know the guys that created it.

In their terms "All intellectual property rights to the User Data remain the property of the User. By entering or uploading any User Data, you grant to GradeProof, to the extent permitted by applicable laws, a non-exclusive, royalty-free, perpetual, worldwide, irrevocable license to use any User Data, as well as feedback and results, for the purposes of:

    Providing the Platform and the Services; and
    For improving the quality of the Platform and the Services generally.

GradeProof has a royalty-free, worldwide, irrevocable, perpetual license to use and incorporate into the Platform any general suggestions, enhancement requests, recommendations or other feedback provided by Users."

A high school level English class?

I mean, this is just an unnecessarily mean comment.

Not everyone has the luxury of going to high school in an English speaking country. Not everyone is strong in English but still need to write properly.

Thanks though.

If you watch Grammarly's advertising, the core market seems to not be English language learners but college graduates that are having a hard time deciding between the usage of "were" and "we're".

https://www.youtube.com/watch?v=Ak-Y56SfkS0

Snark aside, there are plenty of English grammar resources that can be consumed in book form or online without attending an American high school or compromising your privacy. A solid one is the Chicago Manual of Style:

https://www.chicagomanualofstyle.org/home.html

This isn't the type of stuff Grammarly helped me with. Passive voice misuse is still extremely difficult for me to catch. Even after learning about it multiple times.

Not sure how it compares but... https://www.languagetool.org/