[krapp]

There is an open source fork but it runs on Racket[0], so the Arc documentation isn't always correct, and of course that forum and this one differ in terms of features.

[0]https://github.com/arclanguage/anarki

[gus_massa]

HN is written in Arc that is written in Racket.

I think HN use a slightly modified version of Racket with a few tweaks to be more friendly with the high amount of memory used in HN.