I’ll start …
An AS400 back in the early 2000s , used as a legacy system for a leasing company. Some old dude used to come to support it for reporting and other functions. IIRC, there was a nice orange monochrome terminal that was connected to it.
I rarely had to touch it and I left the company before they migrated to a new platform.
I’m sure I’ve ran into more old tech, not sure why this stuck out in my memories.
When I was in local government, they had a load of old sevrers - all sorts of things, most of which I couldn’t identify. There was a mainframe system which was heavily used via Wyse terminals - I’m not sure if it was actually running on a mainframe still at that point, but they definitely had some as I had to change all the backup tapes in lots of server rooms in the building. All sorts of things with what looked like reel to reel tapes in them. Shame even camera phones weren’t a thing (this was in early 2000s) or I’d have taken lots of photos. There were some Sun boxes as well.