Forum OpenACS Q&A: Re: Is using OpenACS or an older version?

It's a very heavily modified version of ACS (predates OpenACS by quite a bit). Looks like it might be 3.4.9, which is dated December 2, 2000.

furfly hosts the site, but all the work on it is done by David Rodriguez, who used to work for Arsdigita. As I recall the site was originally built by Jin.