> Rhombus is an experimental, general-purpose programming language with conventional expression syntax that is built on Racket and that is macro-extensible in the same way as Racket.

It's still work in progress, but you can install and run the prototype. I recomend to take a look at the "demo" file with examples https://github.com/racket/rhombus-prototype/blob/master/demo...

Or read the docs https://docs.racket-lang.org/rhombus/index.html , in particular an overwiew in https://docs.racket-lang.org/rhombus/Modules.html and some examples of macros in https://docs.racket-lang.org/rhombus/expr-macro.html .