IWork

iWork is an Apple application suite available as apps for OS-X and iOS as well as in a cloud-based version on iCloud. It comprises Pages (word processing and desktop publishing), Numbers (spreadsheets), and Keynote (presentations).

The web-based cloud version can be run in a browser (Not all browsers are fully supported; when you try it in Firefox, it says that it is an unsupported browser, but seems to work anyway, though it is possible some features aren't fully functional), and is free for iCloud users. The app versions are paid, though apparently they come free with newly-purchased iOS devices since late 2013; they will sync automatically with iCloud to access cloud-stored documents.

Current versions of the iWork applications can load and save the corresponding Microsoft Office file types (using, apparently, the 2003 file versions): DOC (Word), XLS (Excel), and PPT (Powerpoint). (Apparently earlier versions couldn't, as the Wikipedia article claims a lack of interoperability with Microsoft's programs.) They can also save as PDF, producing a static document that can be useful for viewing, but not so much for editing or import into other software. And then there is the native iWork format, used in slight variations for each of the three applications, and bearing .pages, .numbers, and .key extensions respectively, or double extensions .pages.zip, .numbers.zip, and .key.zip when saved in a ZIP file.

iWork files, when saved under Mac OS-X, are in a bundle format that is actually a directory/folder. Saved in other systems, or exported as e-mail attachments, they are ZIPped and use the double extension as noted above.

File format info
The format has changed between different versions.

Sample files

 * TestSpreadsheet.numbers.zip
 * TestReport.pages.zip
 * TestPresentation.key.zip

Links

 * Wikipedia article
 * Some info on the iWork file format
 * Exploring the New iWork for Mac File Formats
 * iWork 2.0 programming guide; documents early file formats
 * Format discussion