What is MeeGo Harmattan?
MeeGo/Harmattan is a Linux-based open source mobile operating system project that runs the MeeGo 1.2 UX on top of the Maemo6(Harmattan) core.
Nokia N9 - On June 21st 2011, Nokia announced its first MeeGo/Harmattan smartphone device, Nokia N9. More info at http://swipe.nokia.com.
Nokia N950 or Nokia N9 devkit - The Nokia N950 is a platform available for developers targeting the Nokia N9 and MeeGo handset apps in general. Developers working on new or existing opensource applications to be published on Nokia store can apply for the loan of one of these devices. More information are available at MeeGo device-program page.
Nokia allows developers to use Qt SDK used for Symbian and Maemo even to develope MeeGo Harmattan applications. You can read more about MeeGo 1.2 Harmattan SDK here.