A few days ago, Microsoft led the creation of a new organization called OpenXMLDeveloper.org.
The goal of this community is to exchange information about the usage of the ecma-developed Office Open XML file formats. Founding members include Apple, Intel, Toshiba and many others. These organizations have came together to document the formats and enable developers to read and write settings.
To quote - Jan van den Beld, Secretary General, Ecma International “Standardization to foster the growth and openness of file formats across the industry is of benefit to everyone. As such, having an Open XML Formats Developer Group as a community and resource to foster the adoption of the Office Open XML File Formats is great for all participants involved. We look forward to seeing this community grow.”
You can take a look at the Office Open XML Document Interchange Specification here.