This is the website for APL9, which is an APL implementation written in C on and for Plan 9 (9front specifically, but the other versions should work as well).
Work started in January 2022, when I wanted to do some APL programming on 9front, but no implementation existed. The focus has been on adding features and behaving (on most points) like Dyalog APL. Speed is poor, since many primitives are implemented in terms of each other, which is not optimal, but it helped me implement stuff easier.
↫ APL9 website
I honestly have no idea what to say.

Amazing that APL is still alive. The last time I had heard about it was 20 years ago.
Given that I’m putting effort to learn ADA for reasons, I can relate with those who put effort to lear things that are not really in spotlight anymore.
I don’t think any of this is meant for us mere mortals to comprehend. This is god tier computing.
So happy to see plan9(9front) alive
There’s also https://github.com/robpike/ivy by Rob Pike, co-creator of Plan 9.
AFAIR, one needed a special keyboard to program APL. It seems possible these day to stay with a standard qwerty keyboard though.
Running APL on Plan 9 has to be about one of the most niche things ever. Neat!