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.
I worked in accounting at an IT outsourcing firm. We had to have a telnet client installed on our computers so we could connect to the inventory management system. No idea what it actually ran on, but it was a text menu interface with ASCII borders that would turn into letters if your settings were wrong. Also incredibly slow. It always reminded me of dialing into a BBS when I was a kid.