MJF: 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++.

sounds like DIRECTUI.dll to me. it actually IS exposed by Windows Runtime (COM vNext).

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.

sounds like other Windows Runtime components (Windows.*.dll) to me, doubt if they are really part of 'Jupiter' but anyway, its part of the whole picture.

Windows.Devices.Geolocation.dll
Windows.Devices.Print.dll
Windows.Devices.Proximity.dll
Windows.Devices.Sensors.dll
Windows.Dlna.dll
Windows.Dlna.ps.dll
Windows.Graphics.dll
Windows.Media.dll
Windows.Networking.Connectivity.dll
Windows.Networking.dll
Windows.Storage.ApplicationData.dll
Windows.Store.dll
Windows.Store.ProxyStub.dll
Windows.UI.dll
Windows.UI.Immersive.dll
Windows.Web.dll

P.S. DirectUI.dll itself is 'native code', just like agcore in Silverlight.