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 That's cool!
(not trying to drag down, just asking: Is 3.3 open sourced yet?)
@wyatt8740 working on it
@shanselman better answer than I could have hoped for :)
(while I'm asking, any chance of 5.x and/or 6.x?)
Would be cool to see what I'd need to do to port it back to the PC-9801... if the license permits that
@wyatt8740 yes I’m trying to work through them one at a time