Apollo's heyday was a bit before my time, but my first real job was working on technical software at a company who was a big-ticket technical software developer on Apollos (and I even once saw marketing brochure with our badge on an Apollo workstation). As an intern, I set up a pair of them for porting (though we preferred SPARCstations), and later, when I moved to headquarters, HQ was still doing the master SCM and (what's now called) CI, for all platforms, on Apollo DN10k pedestals. We got the DSEE descendant Atria ClearCase on non-Apollo workstations, in a new-tech R&D group I was in. I bought a couple retired Apollo workstations just to play with them at home.
Apollo did a lot of innovative stuff in Domain, and it's one of the few platforms I'm sometimes tempted to buy again, just to play with it and understand more of how they approached things.
When it had been years since I'd seen or heard of Apollo anywhere, I bumped into someone from there, who mentioned that Boeing had done some documentation using Apollos, and part of their very serious configuration management process involved them physically archiving an entire Domain network. (I'm guessing they used the very nice Interleaf software, which seemed to be popular on Apollo, and, by that time, had long also been available on other platforms.) It was appealing to think of an Apollo Domain network preserved in stasis, should humanity ever need to call up Apollo for duty again.