Hypertext on IBM systems is no surprise - the precursor to SGML, on which HTML is based, was introduced on z/OS aka MVS, and to this date is available as SCRIPT/VS on IBM mainframes. Though IBM sold off their printer business over a decade ago and discontinued AFP printing so customers (insurers, banks) went looking for alternatives. The telephone-book sized AIX documentation in printed form was also excellent; I guess (but I'm not sure) it was produced using Iddoc or DITA (also SGML-based cross-publishing tools by IBM).