I'm throwing out this WI as a first step towards a TL where Microsoft accepts open source principles as early as the 1980's.
One of the major outcomes of this TL will be Microsoft becoming a service provider and systems solution company, not unlike Canonical, Red Hat, or IBM. Its non-enterprise versions of OS/2 (yes, OS/2) would be provided for the cost of the media and later for free Internet download. OS/2 code would be freely released. A community of amateur and professional coders would work with Microsoft to continually develop the operating system (akin to launchpad.net).
This will be a rather complex TL. Here are some initial difficulties:
1) Working Richard Stallman's early writings and lectures on the GPL and the open source philosophy into the TL.
2) Have OS/2 (a superior product, in my opinion) triumph over Windows in the late 80's/early 90's
3) Find a way for Microsoft to make a profit in enterprise software and hardware while offering some of its code for open and public development. Perhaps Microsoft might use some proprietary code in its corporate products. MS could then tie closed code into specific lines of hardware.
4) How would Linux/open source BSD fit into this TL?