We just open-sourced DOS 4 (and found binaries of Multitasking DOS 4) https://www.hanselman.com/blog/open-sourcing-dos-4
Open Sourcing DOS 4

See the canonical version of this blog post at the Microsoft Open Source Blog! ...

@shanselman no gwbasic though :/

@mirabilos @shanselman A reasonable chunk of GW-BASIC was released a few years back - I remember reading an OS/2 Museum post about trying to work out which OEM versions it corresponded to, which mentioned the OEM-specifc bits were sadly missing. But there must have been a 'generic' version of that code for the retail versions of MS-DOS to include...

https://www.os2museum.com/wp/gw-basic-source-notes/

GW-BASIC Source Notes | OS/2 Museum

GitHub - microsoft/GW-BASIC: The original source code of Microsoft GW-BASIC from 1983

The original source code of Microsoft GW-BASIC from 1983 - microsoft/GW-BASIC

GitHub
@shanselman @baljemmett thatโ€™s not 3.23 from retail DOS 4 though and lacking