There were a couple of clones, but none took off really. The most prolific one seems to be newmogul.com by nickb, focused on business and economics. Nickb has a

There were a couple of clones, but none took off really. The most prolific one seems to be newmogul.com by nickb, focused on business and economics. Nickb has all but disappeared since, and Newmogul is no more, but some of the patrons moved on to http://markenomics.com http://markenomics.com. HN is written in PG's own dialect of lisp, http://arclanguage.org http://arclanguage.org and source code for vanilla version of the site is included with arc distribution. There's no reason not to hack together a clone and get a taste of the language.