SproutCore is already used for the MobileMe and iWork.com web interfaces. However, it is not the only web app framework Apple uses. Other known projects are Gianduia, Coherent, AdLib, TuneKit and PastryKit.

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Coherent (Dashcode's JS framework): http://coherentjs.org/

AdLib (for iPad): http://almost.done21.com/2010/04/adlib-apples-secret-ipad-we...

PastryKit (for iPhone, iPod touch): http://arstechnica.com/apple/news/2009/12/pastrykit-best-iph...

http://daringfireball.net/2009/12/more_on_pastrykit

Gianduia (for desktop browsers): http://lists.apple.com/archives/Webobjects-dev/2009/Nov/msg0...

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More about the use of these different frameworks:

http://www.appleinsider.com/print/10/05/07/apple_developing_...

Nope.