INTERCAL is a programming language unlike any other, partly due to the efforts of the designers of INTERCAL, and partly due to the efforts of the designers of every programming language created since.
INTERCAL strips away the added layers of modern computer languages, in order to return to somebody else's roots.
INTERCAL is the definitive write-only language.
It has been suggested that INTERCAL is the work of aliens. It has also been suggested that INTERCAL is the work of Chthulhu. Although there is strong evidence that INTERCAL was created by Don Woods and James Lyon at Princeton in 1972, neither of these alternate hypotheses can be dismissed out of hand.
Do this. Imagine FORTRAN and RPG unwisely coupling and spawning a mutant half-wit. Imagine that half-wit being fed a bunch of acid. Imagine that it becomes autistic and decides that it will only communicate with others via a Ouija board.
It's kind of a funny mental image, don't you think?
Seriously, here is a definition.
P.D.Q. Bach is the INTERCAL of Baroque music.
Okay. Seriously (or as serious as is possible), INTERCAL is a computer programming language that was intentionally created to have as little in common with existing languages as was possible for its inventors to attain. In short, INTERCAL was made to be the apex of unprecedentedness.
Inasmuch as this goal is concerned, INTERCAL must be viewed as being eminently successful. Some might interject here that with respect to the goal of making a useful language, INTERCAL lands a bit wide of the mark. This is wholly wrongheaded, because this was never a goal. INTERCAL did not land wide of this mark simply because the mark is in a completely different park than the one in which Woods and Lyon were playing ball. (And a much more crowded one, it should be noted.)
Regardless, INTERCAL is no less Turing-complete than any other programming language you could care to name. It is a completely usable language. And who can say but that someday, someone may find it to be useful also?
(Well, it could happen.)
I can, and have. And so can you. The original compiler, written by INTERCAL's creators, was implemented in SPITBOL on a mainframe, and has long since ceased to be available. However, in 1990 Eric S. Raymond brought INTERCAL back to life with the C-INTERCAL compiler. This compiler is freely available, and is maintained by its author along with "an international community of technomasochists."
Well, the best way to get a feeling for what is INTERCAL is to take a look at the manual. Here is the HTML version of the C-INTERCAL manual. Read it, and then decide for yourself.