Files with a .key extension are created by Apple's "Keynote" application which forms part of Apple's iWork office suite, a set of applications which run on the Mac OS X and iOS operating systems, and also includes Numbers (for spreadsheets) and Pages (for word processing).
Designed to let users easily create, play and share presentations, Keynote contains most of the features found in modern presentation software, such as a slide navigator, the ability to add tables, shapes and charts to slides and a powerful media browser which allows users to drag and drop music from from iTunes, and photos from iPhoto and Aperture into their slides.
Keynote contains a large number of pre-designed themes to let users select common presentation formats, and powerful graphics tools to manipulate embedded images and provide advanced 3D transitions between slides (powered by OpenGL). The major Keynote releases are summarised below:
Version
Date
Key features
1.0
January 2003
First version - basic features - Import Powerpoint presentations, slide navigator, graphics support for rotations, resizing and opacity, charts and slide transitions.
2.0
January 2005
Released in iWork '05. Contained improved animations for slides and text, iLife media browser, new themes, more presenter controls, embedded hyperlinks and the ability to export presentations to Macromedia Flash.
3.0
January 2006
Released in iWork '06 with new themes, HD-capability, improved graphing and table features, cinematic transitions and 3D graphs.
4.0
August 2007
Released in iWork '08 with easier to use animation features, new templates, smart builds (for predefined animations), instant alpha (for removing backgrounds from photographs), and a new narration to add a voiceover to slideshows.
5.0
January 2009
Released in iWork '09. Contains support for MathType equations, a new share menu, trackpad support, "magic move" (for easier transitions), improved presenter tools, but removed support for exporting to Flash.
5.1
July 2011
Added support for Mac OS X Lion, and included support for full screen functionality, auto-save, resume and versioning. Also with improved compatibility with Microsoft Office.
5.2
July 2012
Support added for iCloud documents and Retina displays.
5.3
December 2012
Adds Keynote support for iOS 6.0
6.0
October 2013
Part of new iWork suite for Mac, with 64-bit support and iCloud syncing.
6.1
January 2014
Improved compatibility with Microsoft Powerpoint.
6.5
October 2014
Updated design of OS X Yosemite, iOS 8 and a new file format to improve support for 3rd party online services.
A .key file is actually a compressed ZIP file comprised of a number of other different files combined that together make up a .key file. The most recent version of Keynote saves files with an "Index" directory containing Apple's proprietary IWA file format, a "Metadata" directory with .plist files, a "Data" directory with image assets (e.g. backgrounds and photos used in slides) and one or more jpg files for allowing quick previews.
Files created by Keynote in iWork cannot be opened by programs other than iWork.
As part of Microsoft's 2007 suite another open XML document type was introduced. This time in the PowerPoint sphere, PPTX is a Presentation format that stores slides used for slide shows or presentations; like a normal PPT format it may include text, images, and other media; however PPTX is based on the Open XML format and uses ZIP compression for smaller file sizes
A PPTX file is quite unique. The specifications for PPTX are in the ECMA-376 standard for Office Open XML. You can make a PPTX file by zipping up a directory, but the material in the directory has to match an OPC structure, including subfolders that have the content in XML format. Any application that supports XML can access and work with data in the new file format. Just like the DOCX file format, PPTX improves file and data management and data recovery.
