I used PipeDream on the Cambridge Z88, and only briefly tried it on other platforms under the PipeDream (Archimedes, MS-DOS) and Fireworkz (Windows) names. I think it was a great moonshot of an idea, ahead of its time when you consider Affinity has done the same thing with Illustration/Layout/Photos.
The screenshots of RISC OS bring back fond memories of playing with it in our school computer room (which was mostly BBC Micros but had a few RISC) - mostly playing Lemmings as I recall! It felt pretty cool at the time though
Pipedream always was spectacularly odd, even at the time.
Our first computer was an Acorn BBC B Microcomputer.
I suppose that most of all, it reminds me of time when actual, real innovation in UI design was still on the menu.