Following recent shared source a new announcement was made today:

Brad Smith, Steve Ballmer, Ray Ozzie

Broad-reaching changes to Microsoft's technology and business practices will increase the openness of its products and drive greater interoperability and opportunity across the IT community

Microsoft Interoperability Principles

1) ensuring open connections;

2) promoting data portability;

3) enhancing support for industry standards;

4) fostering more open engagement with customers and the industry, including open source communities.

 

Chris Maunder
The Code Project

writes on 25/8:

The big news in the {Windows] development community... is the announcement by Microsoft that they will be publishing all of the APIs and communications protocols for its high volume products, including Windows Vista and Office 2007. I remember fondly the days of trying spelunk win32 and I imagine there is many a programmer out there looking forward to getting a firmer grip on these two platforms.