I've seen two systems (not pure software, but
integrated systems)
that really blew me away years ago. My memories of both are very
fuzzy. One was an ECAD workstation called Daisy; it was a schematic
capture system and may have done other things as well. It was
gorgeous but I didn't see much of its capabilities. I saw this
around 1985 or thereabouts.
Daisy was one of the first ECAD workstations. Started out as 8086
Multibus up through 386. I never saw the earliest version of the OS. The
later ones were unix-like. Last versions were Intel 386 PC based. Apple
used them before switching to Valid or Mentor, depending on the project.
I saw parts of a Calay at a surplus place in the mid 90's. There was
also Racal/Redac PCB layout systems. I think I still have the packs from
one of these. It ran RSX11 on an SMS disc controller.
Most of the small stand-alone systems disappeared once IBM PC ECAD
systems developed. There were one or two companies selling CAD tools
into the Macintosh market, but they were pretty awful. There was one
system that was popular for schematic capture on Macs that was used
internally at Apple up through the late 90s.
DEC used a schematic capture system from Stanford through the 70's and
early 80's (SUDS, Stanford University Drawing System). The MIT CADR was
designed using this as well.