While OOXML/ODF war starts to heat up, Microsoft published new version of their another document format "Word 2007: Rich Text Format (RTF) Specification, version 1.9":
The Rich Text Format (RTF) Specification provides a format for text and graphics interchange that can be used with different output devices, operating environments, and operating systems. Version 1.9 of the specification contains the latest updates introduced by Microsoft Office Word 2007.
If somebody forgot, RTF is proprietary but widely supported non-XML document markup format, which looks like this:
{\rtf1\ansi{\fonttbl\f0\fswiss Helvetica;}\f0 Hello!\par This is some {\b bold} text.\par }...