.KEYNOTE File

The keynote file extension is associated with Apple Keynote, a presentation software application developed as a part of the iWork productivity suite (which also includes Pages and Numbers applications) by Apple Inc.

The Keynote Presentation is XML based and may contain basic text documents or elaborated multi-page brochures, including images, special texts, tables, graphs, charts and more. be created from a blank page or based on saved template.

The keynote file is basically a folder named as document_name.keynote that  main presentation document, previews and some metadata. This file format was used in earlier versions of Keynote up to Keynote '06.

The latest versions of iWork Keynote use the key file extension instead. Keynote '09 is also able to save files in keynote format, but you have to change the presentation preferences for that. 

This keynote file type entry was marked as obsolete and no longer supported file format.

This type of file is no longer actively used and is most likely obsolete. This is typically the case for system files in old operating systems, file types from long discontinued software, or previous versions of certain file types (like documents, projects etc.) that were replaced in higher versions of their original programs.

How to open:

Use Keynote application from Apple's iWork office suite to open *.keynote files.However, latest Keynote has sometimes problem with opening older *.keynote presentations.

How to convert:

Normally KEYNOTE file format cannot be converted to other presentation formats with all its features. However, Keynote offers the possibility of exporting the presentation to MOV movies, and to PowerPoint PPS format, albeit at the cost of quality.