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).