What is the use case for this?

I used it to write a macro processor for C which allowed me to write some macros with s-expressions and have it expand to a lot of C code. That way I could actually write real macros for C.

I have also written GUI apps for various things. Kind of like what I did with TCL back in the day.

I wrote a little maths game for my son.

I also wrote a static site generator in it that allowed me to execute racket code at compile time (interpreting each markdown file as a source file).

It's a general purpouse language. Reusig an old comment, I used it for

* A bot to reply emails that uses IMAP, SMTP and web scrapping. (It's not 100% automatic. It replies only the easy cases and adds labels so I reply the tricky ones.)

* An program to cleanup Moodle backups that uses gzip and xml. I compiled it and send it to my coworkers. (The backups have too much info, so before restoring it in another site it's better to remove the unused parts.)

I wrote custom language for designing Age of Empires 2 Random Maps. Basically AoE2 already supports it, but the underlying language is very very primitive. While I am not aware of anyone actually using what I made, it was mostly nice learning experience. https://github.com/Erbenos/aoe2-rms

Because its on top of Racket, you get usual high-level language faculties for basically free.

https://blog.cloudflare.com/topaz-policy-engine-design/

As the other reply said, it is general purpose. It has a focus on education tooling, and language design (languages can be easily implemented on Racket)