OneNote is a free (gratis, not libre) cross-platform note-taking application. An API exists allowing developers to create apps which allow users to create OneNote notes in their own notebooks. Users can use the free application on Windows, Mac OS X, Windows Phone, iOS, Android, and the web. It gathers users' notes (handwritten or typed), drawings, screen clippings, and audio commentaries.
A OneNote service API exists which enables developers to create notes in users' OneDrive notebooks and includes features such as OCR and URL screenshots.
Unlike other MS Office products its file format is binary (see MS-ONE and MS-ONESTORE).
There is also a COM API which enables developers to interact with documents open in a local instance of OneNote on Windows.
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