Telling only part of a story can be worse than keeping completely mum, as Microsoft officials seem to be discovering with Windows 8.
Jupiter is a user interface library for Windows and will allow developers to build immersive applications using a XAML-based approach with coming tools from Microsoft. Jupiter will allow users a choice of programming languages, namely, C#, Visual Basic and C++. (Hey, maybe this is why Microsoft is calling the next version of Visual C++ "WinC++"?)
Microsoft is still going to support Silverlight with Windows 8, and not only as a browser plug-in, my sources say.
Microsoft's longer-term goal is to align its various developer stacks, giving it a story that's comparable to Apple's. Because Apple supporting iOS on tablets and phones, Apple developers can write once and have their apps run in both places with relatively little modification.
Windows Phones are running the Windows Phone OS, which is currently based on the Windows Embedded Compact kernel (with a whole lot of customization), and Windows 7 on tablets. Microsoft's ultimate goal -- now that Windows 8 will be able to run on ARM -- is to get its phones running on Windows, too. It's uncertain whether Microsoft will be able to pull this off by late 2012, when Windows 8 and Windows Phone 8 are both expected to ship.
At the more granular and immediate level, Jupiter is the way that Microsoft is planning to get developers to write new "immersive" applications for Windows 8 that will use the IE 10 rendering engine while using the .Net and Silverlight technologies they already know. Jupiter is aiming to provide these developers with a managed code XAML library, so that developers can access the sensors, networking and other Windows 8 elements in a way to which they're accustomed.
I believe Jupiter is key to enabling Microsoft to continue to insist that Silverlight's not dead (as far as a development platform) -- at least for now. But anything that's not a new Windows 8 "immersive," modern application, going forward, is now going to be considered "legacy," from what I can tell.
All of what I've said here is from sources who have asked not to be identified, not from Microsoft officials associated with Microsoft's Windows or Developer Division. Like many devs I've heard from, I don't believe Microsoft can't afford to wait three more months to let its developer base know what its intentions are. So far, however, ill-advised silence seems to be the Softies' plan....