[krapp]

Because it's owned by billion dollar Silicon Valley startup incubator and has a ton of "business logic" for YC baked into it, and it isn't worth anyone's time to bother open sourcing it. Dang has mentioned wanting to do it but it isn't a priority.

You can get the original version of Arc Lisp and the forum it's based on here[0], which only a select few people update, rarely, and they don't take PRs as far as I'm aware. And there is a FOSS fork here[1], which might as well be dead, but as far as what's actually running under HN's hood, good luck getting to it if you aren't a YC employee.

[0]http://arclanguage.org/

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