Try as they might to project a monolith image, there isn’t one Apple — there’s multiple silos each containing multiple teams.
SproutCore is used by the MobileMe team. Publicly advertised, targeting desktop-class web applications. Chief competitor: Cappuccino. (IMO SproutCore’s gem is the DataStore layer. To my knowledge, nothing has caught up with it yet.)
Gianduia used by Apple retail. Not advertised yet, but you can see a demonstration on Apple’s One to One (requires buying a new Mac+contract) or for a limited time their holiday retail reservation system. As I previously tweeted, Gianduia is like SproutCore in that it targets desktop-class web apps.
TuneKit is a small publicly-advertised framework for targeting WebKit-in-iTunes. Published by the iTunes team.
Coherent is the publicly-advertised framework blessed by Dashcode 3. Developer tools team.
PastryKit is an Apple-internal framework focusing on iPhone-style UI in a WebKit view. Used by the iPhone team.
Thanks to Pascal Robert for suggesting some of these team categories. It was at Pascal’s WOWODC 09 that I learned about Gianduia.