DevSummitAGSilverLight is a project mainly written in C# and JAVASCRIPT, it's free.
This is a mapping application that I built for the 2011 Esri Developer Summit. It uses the ArcGIS Server Silverlight API and sample Esri ArcGIS Server instances.
This app was created for the Esri 2011 Light Up the Night Challenge
This is a Silverlight Application with the ArcGIS Server API.
This API requires several development tools which can be found on this page: http://help.arcgis.com/en/webapi/silverlight/help/index.html#/System_requirements/01660000000t000000/