Thinking in an array language (2022)

Previously:

Thinking in an array language (2022) - https://news.ycombinator.com/item?id=38981639 - Jan 2024 (152 comments)

Thinking in an array language - https://news.ycombinator.com/item?id=31377262 - May 2022 (66 comments)

Giving APL a quick glance I find the topic at least intriguing.

So if I understand this right K is one of the more popular/recommended APL-derivatives nowadays. K is proprietary but there are a bunch of compatible implementations which are themselves open source. Is that correct?

Which APL derivatives (with an active/healthy userbase) besides k would you recommend to take a closer look at?

I still haven't used K/Q/etc. because they look insane, but the more I read about them the more it seems like they are basically the maths equivalent of regexes. Super terse and powerful. Pretty much write-only. Very useful for interactive use, definitely. But if you find yourself hitting "save" on a regex that's a red flag and if most of your program relies on regexes something has gone very wrong.