Congratulations to the Windows SideShow team on the release of the Windows SideShow Device SDK 1.4!
Windows SideShow is a technology that lets users write small gadgets for external displays. The SDK includes a simulator so you can start working with your code right away, even if you don't have a SideShow device.
I've only worked with the native SDK (C/C++) but it was pretty easy to write gadgets. Writing code for the display is similar to writing a webpage, except it uses SCF (simple content format) which resembles a basic subset of HTML. The gadget logic is written in C/C++ or C# and is where the SCF is generated and sent up to the SideShow display device.
For more info, check out the Windows SideShow team blog: http://blogs.msdn.com/sideshow/archive/2008/01/23/it-s-here-announcing-the-windows-sideshow-device-sdk-for-net-micro-framework-v1-4.aspx