It’s very fun as low-level languages go. I like gforth[1]. If you want modern high-level languages in the same family, look into “concatenative programming”. In particular, Factor[2] is a cool Smalltalk-like object-oriented concatenative language with a nice interactive environment. It’s still under somewhat active development, but they could really use more users to drive progress.
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.
Is Factor still being maintained? I seem to remember that the 0.97 release came out some years ago, and it's worrisome (in terms of investment of time in learning a new language) to think it might be frozen pre-1.0 release.
Yeah, there’s still a steady trickle of maintenance work by a couple of guys. The latest commits were just a couple weeks ago. It’s just that no one has taken the time to put together an official release lately, and it seems like calling it 1.0 has sorta been “somebody else’s problem” for a while now, partly because the original author is no longer involved. Like I said, I think what they really need is motivated early adopter–type users to provide an incentive to improve it.
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.
There’s also an IRC channel[1] and I’m the mod of a subreddit[2] for people interested in the paradigm. They both have fairly low/intermittent traffic but there’s a small group of dedicated people, some programming in Factor, several (myself included) working on their own languages.
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.
It's fun to learn, and one of the first interpreted environments. What it enables is quick development on platforms with modest resources! Instead of compiling and executing you could develop quickly! Haven't used it for anything more than to do some examples in some tutorial.
One thing that's nice about the language is that it's the simplest language you can implement on your own without going insane!
I've never found a compelling use for FORTH, but I've loved it since I was first exposed to it. The idea that you can define your own "words", essentially writing your own syntax, is very seductive.
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.
Ah, the joy of telling someone to hold down Command+Alt+O+F while booting just to eject their CD... (weirdly enough the most frequent Open Firmware use case on Macs)