Making languages is the thing that Racket does better than any other language, so they do tend proliferate. However, for getting stuff done the majority of work is done in just Racket. You don't need to know the other languages unless you're interested in some specialist task they target.
Back when I was a regular Scheme user Racket had by far the biggest ecosystem and community, so it would be my suggestion if you're interested in exploring Scheme.
Yes. I've written a test framework for another software I'm developing that (optionally) sets up an environment for the executable under test, (optionally) launches and monitors the executable (process state, stderr/stdout), connects to the process via a WebSocket (that's what that executable does) and then tests the surface of the exposed WS-API. As the executable runs under windows & linux, embedded and not, this approach lets me run the test suite under all different hosts and connect to localhost or the thing running elsewhere. So, in my case, you may not see it in a product; but the product we're building is continuously tested with a myriad of racket programs.
I did and even though I'm forever in love with both Rebol and Red, Racket does languages in a more fun way and powerful way for my own personal taste. Don't know if you have checked this book out but https://beautifulracket.com/ is a wonderful introduction for building languages with Racket.
For me, the power of the Redbol approach lies in the rich set of datatypes, so you can create dialects at the block/value level, leveraging the syntax without having to tokenize at the string level. It's no small thing to be able to create languages that natively understand values like email addresses, URLs, IP addresses, files as distinct from strings, and more.
From brief check on the book I see that Racket has a lot of infrastructure for making languages, but fundamentally I don't see the difference with Parse in Red. One can easily add tokenizer, reader and expander similar to what is there in Racket.
For those that haven't used Rebol or Red. It is a homoiconic language like lisp, but no s-expressions as I understand it.
Rebol is really nice with a lot of built-in primitives that make it super useful although Rebol is kind of dead now (some users exist, but no new versions in a while). Red is being worked on and if it ever reaches 1.0 could be a game changer.
I think it is pretty easy to build little DSLs, but I don't think macros are super easy unless I'm mistaken. If somebody could shed some light for me I'd appreciate it.
You don't need macros in Red (but it's easy to roll out your own macro layer, if one so desires [1]), all code transformations can be achieved at runtime. A brief explanation of how this works is given in [2].
As for Red / Rebol vs. Racket content - I wrote an excessive post on that some time ago [3], in response to similar question.
TL;DR from language creation perspective is that Racket has state-of-the-art macro system and all the necessary infrastructure, and Red has metaDSL (that is, DSL for creating DSLs) called Parse [4], which is basically PEG on steroids (think OMeta) + a different take on homoiconicity, compared to Lisps, which, most of the time, renders custom readers and tokenizers unnecessary.
I tried it and would consider it a write-once language, similar to Forth in that respect. It seems good for quick hacks but not for long-term maintainable projects.
I'd like more info on that as well (as part of Team Red). And, for comparison, what language(s) you feel are best for that, and what features lead to that.
where both `cat` and `grep` can be either shell commands or Red functions and you can redirect input/output from/to variables as well as files. Also you can mixin Red data types, like in example here `%/etc/passwd` is a file instance, not a string.
Also the language itself heavily utilizes this (called Parse dialog) for example they don't have regular expressions at all, JSON is parsed using it as well, GUI system is a fully separate dialog and so on.
Back when I was a regular Scheme user Racket had by far the biggest ecosystem and community, so it would be my suggestion if you're interested in exploring Scheme.