FreeBSD bootloader uses Forth:

https://www.freebsd.org/cgi/man.cgi?query=loader&sektion=8

Also, while it's not Forth, it could be argued that the RPL language as used on HP scientific calculators, is a kind of higher-level Forth produced by cross-breeding with Lisp. Indeed, its name, while officially not an acronym, originated as "Reverse Polish Lisp". Its implementation is also kinda awesome, because it has two layers - User RPL, which is more high-level and completely memory-safe, with error checking everywhere, and is exposed directly to calculator users; and System RPL, which basically just compiles the source directly to a bunch of call opcodes (so if you mismatch the stack at any point, it just crashes), and which is used to implement the calculator OS and stock apps, as well as User RPL.

http://www.hpmuseum.org/rpl.htm

Yes, but its heyday was the 70s through mid-80s. The most recent use I'm familiar with was the OpenBoot firmware in OLPC laptops, though I've been out of it so long I wouldn't know what's current.

Anyone that worked with Sun Sparc hardware probably remembers the PROM monitor(SUN's BIOS basically) which was written in Forth and had a Forth interpreter. There's a couple of questions on this FAQ about Forth:

http://sunsite.uakom.sk/sunworldonline/swol-10-1995/swol-10-...

Not as much nowadays as back when embedded computers were severely memory-limited. In those days, you could use Forth and get a semi-high-level, interactive REPL language with a resident compiler in a few K of memory. Now you would usually just use C or Python because memories are huge.

While we're on the subject, Forth is interesting because as a stack-based language, it forces you to structure your programs as function compositions. This was not a popular idea in the 80s, but with the increasing popularity of functional programming, it's relevant again.

One more I forgot: Postscript (the full language of which PDF is a simplification). It's not Forth per se, but it's very Forth-like in much the same way Clojure is Lisp-like.

I know of at least 2 commercial implementations: VFX Forth by mpe[0] and SwiftForth by Forth Inc[1]. Both companies are still in business, selling their tools for hundreds to thousands of dollars, so there is obviously some people using them. I think they have a partial customer listing somewhere on their site. Oh, and there's also gforth of course.

Then again, part of the charm of forth is how easily it is to bootstrap your own forth on your own system. There could be countless homegrown forths out there, in addition to these commercial offerings.

I haven't used forth for anything in production, myself. I just think it's a really interesting language. It's a great "what if" question. What if everything built on C had been built on Forth instead? What if all the work in improving the C language, tooling, operating systems, libraries, hardware etc had been spent improving Forth and stacks instead? It's fun to ponder.

If you want to read more about forth, check out Thinking Forth[2]. It's really got some great insights about programming and software design in general, not just applicable to forth programming in particular.

Starting Forth[3] is also good more of a beginner's introduction to forth. And Moore's own Problem Oriented Language is a good book talking about what his intentions were when he created forth[4].

For more reading: This page has a lot of good forth links too [5] Chuck Moore's color forth blog[6] This site has lots of interviews with Chuck Moore on it and other forth opinion pieces[7] Forth Interest Group site[8]

There's also a new forth standard that's being worked on[9]. Seems pretty active, too.

[0] http://www.mpeforth.com/software/pc-systems/vfx-forth-for-wi...

[1] https://www.forth.com/swiftforth/

[2] http://thinking-forth.sourceforge.net/

[3] https://www.forth.com/starting-forth/0-starting-forth/

[4] http://www.forth.org/POL.pdf

[5] http://www.complang.tuwien.ac.at/projects/forth.html

[6] https://web.archive.org/web/20160305013837/http://www.colorf...

[7] http://www.ultratechnology.com/

[8] http://www.forth.org/

[9] https://forth-standard.org/