Microsoft just released the source code of MS-DOS 2.0 and Word 1.1a. If this is obvious that you will never run these programs again on your own machine, this is pretty cool to see the evolution of software development! Word source code contains some assembly code while MS-DOS 2.0 is solely written in Assembly. This is something nobody would consider today, especially considering portability and maintenance concerns!
Having a look at the source code is definitively worth it and I invite all my fellow geeks to have a look at it!