I used that for a few years outputting slides to transparencies on a pen plotter. There was some other pre-Powerpoint program I used on PCs back then too but don't remember the name--may have been Lotus Freelance. (And a minicomputer-based program before those.)
Those were the days when you had all manner of different word processing and graphics programs (among other things--though Lotus had mostly standardized people on 1-2-3 before Excel and Microsoft Office came along).
It's been decades since I heard of Harvard Graphics. Was part of my toolkit with WordStar, Lotus 123, FoxPro and NC. MS C6.0, MASM, CodeWarrior, an editor called Brief on the dev side. Good times.
I remember getting a giant box copy of it when a company my dad worked for was shutting down, it was years after it had been released but it had a massive manual and was pretty powerful.