The ones I remember were all books. At the time, I thought this was one of the best books available: http://www.amazon.com/APL-Interactive-Approach-Leonard-Gilma... -- but I don't know if I'd pay $522 for it... actually I do know, and I wouldn't. The paper covered versions are just fine, and a much better price :-)
EDIT: I just opened the drop down on the paper covered versions. Prices between $34.13 and $1806.23!!! Is that real?!? Wow, I had five or six copies of something that seems to be incredibly valuable. Too late for an insurance claim on that basement flood.
All the decent tutorials that I know of were in book form. Unless someone's scanned them they're gone. I know mine got destroyed in a flooded basement.
If my memory hasn't been completely corrupted by background radiation, I've seen papers as early as the mid 1950s about this notation.
APL started out as a notation for expressing computation (this is not precise but good enough). As far as I'm concerned it's sitting at a level of abstraction higher than Haskell (arguably like a library overtop Haskell).
Now, in the theme of this thread, APL was able to achieve all of this given the constraints at the time.
The MCM/70 was a microprocessor based laptop computer that shipped in 1974 (demonstrated in 1972, some prototypes delivered to customers in 1973) and ran APL using an 80 kHz (that kilo) 8008 (with a whole 8 bytes of stack) with 2 kBytes (that's kilo) RAM or maxed out at 8 kB (again, that's kilo) of RAM. This is a small slow machine that still ran APL (and nothing else). IEEE Annals of Computer History has this computer as the earliest commercial, non-kit personal computer (IEEE Annals of the History of Computing, 2003: pg. 62-75). And, I say again, it ran APL exclusively.
Control Data dominated the super computer market in the 70s. The CDC 7600 (designed by Cray himself, 36.4 MHz with 65 kWord (a word was some multiple of 12 bits, probably 60 bits but I'm fuzzy on that) and about 36 MFLOPS according to wikipedia) was normally programmed in FORTRAN. In fact, this would be a classic machine to run FORTRAN. However, the APL implementation available was often able to outperform it, almost always when coded by an engineer (and I mean like civil, mechanical, industrial, etc engineer, not a software engineer) rather than someone specialising in writing fast software.
I wish everyone would think about what these people accomplished given those constraints. And think about this world and think again about Bret Victor's talk.
EDIT: I just opened the drop down on the paper covered versions. Prices between $34.13 and $1806.23!!! Is that real?!? Wow, I had five or six copies of something that seems to be incredibly valuable. Too late for an insurance claim on that basement flood.