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I think BQN is a lot of fun, it is an array language like APL, but it does some things different https://mlochbaum.github.io/BQN/ the documentation is great.

Dyalog APL is more of an actual APL, https://www.dyalog.com/

There is also J https://www.jsoftware.com/#/

The array language community on discord "The Apl Farm" (https://discord.gg/SDTW36EhWF) is pretty active.

I also love the Arraycast podcast https://www.arraycast.com/ many amazing interviews and interesting discussions.

Start here (disclaimer: author) https://xpqz.github.io/learnapl/intro.html

I think the j learning materials are best, particularly 'learning j' (https://www.jsoftware.com/help/learning/contents.htm), though others like 'j for c programmers' (https://www.jsoftware.com/help/jforc/contents.htm).

There is a book on Klong https://t3x.org/klong/book.html

I've been using klong as it is small, quick to build and has good intro, reference and quick-reference.

One downside is somewhat memory limited.

To add to the list, this one is pretty good;

https://github.com/razetime/ngn-k-tutorial

https://apl.wiki/Learning_resources

Head on over to apl.chat! People are really friendly over there.