Some random nightly news, MS Word for Windows 1.1, and DOS 1.1/2.0 specifically.
A snippet from the Computer History Museum website:
“MS-DOS and Word for Windows built the foundation for Microsoft’s success in the technology industry,” said Roy Levin, distinguished engineer and managing director, Microsoft Research. “By contributing these source codes to the Computer History Museum archives, Microsoft is making these historic systems from the early era of personal computing available to the community for historical and technical scholarship.”
I found these sources interesting to look through during a cup of coffee, you can spot the odd cussing code comment, and really see what coding was like back then when WYSIWYG word processors changed the world.
To download the sources, you may select which one you desire on the page and you will find an agreement and download link.