Microsoft made available the source code for its first edition of Microsoft Word.
The 7 MB zip file contains 1021 files in 33 folders. In the root directory there is a “readme” file that briefly explains the rest of the contents. Most of it is source code in C, but there are also text documents, x86 assembler-language source files, executable tools, batch files, and more.
To access this material you must agree to the terms of the license displayed here, which permits only non-commercial use and does not give you the right to license it to third parties by posting copies elsewhere on the web.
About 1000 files, will look further into it.