From The Reg:

Microsoft revealed that it will publish the APIs for Windows Vista, Server 2008, SQL Server 2008, Office 2007, Exchange Server 2007 and Office SharePoint Server 2007 on its website. “Developers do not need to take a license or pay a royalty or other fee to access this information,” the company said. “Open access to this documentation will ensure that third-party developers can connect to Microsoft’s high-volume products just as Microsoft’s other products do.”

In addition, Microsoft will release some 30,000 pages of documentation surrounding Windows client and server protocols. In the past, partners and customers needed to acquire a trade secret license to this information through the Microsoft Work Group Server Protocol Program (WSPP) and the Microsoft Communication Protocol Program (MCPP). Similar protocol reveals will occur for Office 2007 and other “high-volume products” in the coming months.