MSDOS 6.0 might be interesting. Windows 3.1 too. And MS-DOS 4.0/4.1, not to be confused with 4.00/4.01, which had multi-tasking features: https://en.wikipedi

MSDOS 6.0 might be interesting. Windows 3.1 too. And MS-DOS 4.0/4.1, not to be confused with 4.00/4.01, which had multi-tasking features: https://en.wikipedia.org/wiki/MS-DOS_4.0_(multitasking) https://en.wikipedia.org/wiki/MS-DOS_4.0_(multitasking)