More senior than Windows itself, and still runs the world
Microsoft Excel, the true successor to the throne of COBOL. Version 1.0 was released on the last day of September 1985, four decades ago.
Since the original US English version of Windows 1.0 went to manufacturing at the end of November that year, this means that the default spreadsheet for Microsoft Windows is itself older than Windows. (The European version of Windows didn’t appear until May 1986, but that doesn’t really matter, nobody cared about it either.)