Both "ductulators" and "system syzers" are circular slide rules that predate computers & software. They were/are popular with people doing HVAC work. I've never done much with ducting, so I don't know if they've got software - but they no doubt do. The system syzer from Bell & Gossett has been available as software for years.
I've still got the old circular slide rules, though I haven't used them for a long time.