FreeDOS, the free and open-source alternative to Microsoft DOS (MS-DOS), just released a new major update. It still has excellent compatibility with MS-DOS software, including Windows 3.1 and earlier, ...
Microsoft’s MS-DOS (and its IBM-branded counterpart, PC DOS) eventually became software juggernauts, powering the vast majority of PCs throughout the ’80s and serving as the underpinnings of Windows ...
TL;DR: Microsoft will likely never release the original source code of Windows into the wild, but the company is clearly interested in sharing important episodes of its software development history.