iWork is the Mac equivalent of MS Office.
The contents of an Index.zip file includes a Tables folder and a set of IWA files (iWorks Archive format). This format uses Snappy Compression (an open format developed by Google) using the framing format. It is a package format contained in a folder where the name of the folder is the document name. For distribution this folder and its content are normally zipped.
|Tables||a folder containing DataList.iwa|
|CalculationEngine.iwa||binary file includes the language identification|
|Document.iwa||binary file containing the text in nearly clear text (uncompressed).|
|DocumentStylesheet.iwa||binary file containing the style sheet.|
|Metadata.iwa||binary, top level document pointing to all the other files.|
|ThemeStylesheet.iwa||binary file - master stylesheet|