Office 2010 and related products are currently available for technical preview by invitation-only. While the products won’t be widely available until 2010, Microsoft’ve already published, in conjunction with the technical preview, thousands of pages of detailed technical specifications for the protocols used by Microsoft products to communicate with Office 2010. The documentation describes each protocol in detail, including technical requirements, limitations, dependencies, and other protocol behavior. Anyone in the world with a web browser is free to review it anytime they want without charge, revealed.

More info: Microsoft Office Protocols (MSDN) | Download (.zip)