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OOXML stands for the Open Office XML. It was developed by Microsoft, and is used as the file format for Office 2007 applications. This is not related to the open source OpenOffice applications.
XmlLite is a library for high performance XML applications. It is shipped as a DLL. XmlLite comes with C++ support. You can use it out of the box with Microsoft Visual Studio 2005. It does not do XML validation (to achieve high performance).
XAML stands for extensible application markup language. It is used a lot in the .NET framework. Specifically it is used in WPF, Silverlight, and WF.