I'm working on porting a foxpro database from 1988 that's running an active business which I won't talk about much before it's done, and have actually encountered in Costa Rica an auto parts shop in one of the sketchiest parts of the capital city of this country with a green on black phosphor screen running what looked like dBase III for what they were doing on old IBM PCs.
It's pretty crazy what's out there still. I think the one everyone here is familiar with but might not know is really ancient is the travel booking systems for your plane tickets and accommodations, dating back to the 1960s:
Karsten Nohl - Where in the World Is Carmen Sandiego? (33c3) [1]