A secret UI design project at Apple has been outed as a new version of Xcode, according to Daring Fireball's John Gruber.
A few times since January 2009, Ive mentioned Marble, a secret UI design project at Apple which I believed was a new system-wide theme for Mac OS X. E.g.: my MWSF 2009 predictions, and my WWDC 2009 predictions. Ends up I was wrong about what Marble is and in fact, it was announced at WWDC 2010 this month. Its Xcode 4.
Xcode 4 is still in beta and Apple hasn't posted any screenshots; however, developers can get a sneak peak by watching the WWDC 2010 "Developers Tools State of the Union" session.
Gruber also reveals that OS 3.2 for the iPad was not developed by a secret separate team. The real reason iOS 4.0 doesn't support the iPad is due to timing issues. He believes that iOS 4.1 will bring OS unification across all devices.