I recently learned that a web app I wrote in 1999 (for Internet Explorer lol) is still in use by the company I wrote it for. And this app was basically a graphical front end sitting on top of a mainframe application that dated to the 1970s, so my app's continued existence means that mainframe POS is still running, too. My app was written in Classic ASP and Visual Basic 6 - I truly pity whatever poor bastard has to keep supporting that shit. They probably have one ancient PC in a closet somewhere acting as the server for it.