Re: The older the OS...
> I would love to see Windows 3.11 made to work
Good gracious, really? No thanks!
I can think of a dozen OSes from Þe Olde Times I'd rather see put out there for an update.
Windows 2000 on a modern computer would be quite nice. I long hoped that the ReactOS folks would get there some day, but if they did, I think a Microsoft sue-ball would leave nothing but a smoking crater.
Win2K is of course just Windows NT version 5, and since MS is still selling Windows NT, it's not going to make any version of NT FOSS. But by this point, it could certainly release all versions of DOS right up to MS-DOS 6.22 and all versions of 16/32-bit Windows, from 1.0 to Windows ME, without giving away any commercially-significant IP.
And if MS were to let all 20th century versions of Windows be made open source, then it could do a deal with IBM and release OS/2 as well.
OS/2 was great in about 1992. If IBM was unwilling to release the IBM-only x86 OS/2, which is after all still on sale, perhaps it could release Workplace OS/2, the IBM-only PowerPC edition.
That ran on Mach. Mach is still maintained, and Apple still releases the Darwin source code.
Or how about BeOS, still clutched tightly by Access Ltd of Japan, not even slightly well-known for writing the web browser in the Amazon Kindle.
Access also owns PalmOS, including PalmOS Cobalt, released but never shipped on any hardware.