What is the oldest commercial MS-DOS program that can run on modern versions of Windows (such as Windows 8.1 or Windows 10) without third-party emulators?
The 32-bit versions of Windows can still run many DOS binaries directly, using NTVDM, and VisiCalc stills works. VisiCalc was available at launch with the IBM PC, so is probably qualifies as the oldest commercial DOS program which can still run on modern versions of Windows without third-party software.
I ran DOS 1.x basic on modern hardware, in Windows 7. You can run it in any directory, but you can't exit command.com without closing the window.
The package of BASICA that I did and loaded on Vetusware, all were converted in DOS 5.00 vm, and tested in the DOS sessions of Windows 2000 and Window 7.