Didn't the old Sun workstations boot into a Forth interpreter?
Concatenative programming exposes you to a new style of thinking—IMO it’s the perfect marriage of imperative and functional programming, because you can reason about your code either way: as a “pipeline” composition of functions, or as a sequence of imperative operations on the data stack. In terms of PL theory they have a bunch of elegant algebraic properties too.
It seems to be useful & stable enough for real work, although I have an ulterior motive as well. I work on Kitten, a statically typed concatenative language (Factor : Smalltalk/Lisp :: Kitten : OCaml/C), and I’m hoping to (finally) get out an initial release soon. So I have an incentive to tell people to use Factor, to get more people interested in the paradigm so they go seeking other offerings if they find it interesting/useful but Factor isn’t a good fit.
[1]: irc://freenode.net/#concatenative
What Forth is best at is boostrapping from bare metal to a reasonably high level language with the simplest design possible. Forth was first written at a time when there was a staggering amount of hardware in existence, so reimplementing the base language as quickly as possible was a huge plus. It's got a low floor but a high ceiling. It is a free-wheeling language that allows both very clever and very stupid things.
Unfortunately, this legacy means lots of fragmentation. There is not one cohesive community or set of standard libraries. Forth is very much a "do it yourself" language.
Forth can be very concise because all parameters are passed implicitly on the data stack by default. Parameters and arguments lead to a lot of duplication of expression in traditional languages because you need to give them explicit names both inside and outside the function.
If you prefer, it helps to treat it as a functional language where all functions take a stack and return a stack. All programs are a space separated list of function names. Of course, nothing stops you from using all the global variables you want.
One thing that's nice about the language is that it's the simplest language you can implement on your own without going insane!
You make that sound like it's a BAD thing...
I've written a couple of intepreters for the language, in Perl, in C, and used it on cheap ESP8266 chips, but its something that's more of a fun diversion than a practical/useful thing for me.
So in short "Yes, it is fun", but I'm not so sold on it being "useful", except that learning new things is almost never a mistake.