Microsoft has announced a new .NET API for working with the Open XML file formats. The SDK for Open XML is a free download, and provides a set of typed parts that correspond to the parts in an Open XML document, as well as classes for the package itself and the various document types. The diagram below shows some examples of the types of classes provided in the API:
Documentation for the new API is available on MSDN, including a variety of code samples. More information about the samples can be found on Erika Ehrli's blog.
Microsoft released the technology preview version of this API to get feedback from developers to help guide the future direction of Microsoft's Open XML development tools. You can provide feedback, and also get questions answered, at the MSDN support forum for the SDK. (That's Microsoft's official support forum, but you can also post questions in the Forums section of OpenXmlDeveloper.)