ArcGIS Extensibility SDK for Silverlight
ArcGIS Extensibility SDK for Silverlight 3.2 could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this software available. The most popular versions among the program users are 3.2, 3.1 and 3.0.
This free program is an intellectual property of Environmental Systems Research Institute, Inc. The program lies within Development Tools, more precisely IDE. We cannot guarantee that the program is safe to download as it will be downloaded from the developer's website. Before launching the program, check it with any free antivirus software.
From the developer:
ArcGIS Extensibility SDK for Silverlight is a free program that provides the components needed to create add-ins that extend the ArcGIS Viewer for Silverlight with custom functionality. It contains methods for interacting with application components and properties, including the map, pop-ups and application settings.
You may want to check out more software, such as ArcGIS Runtime SDK for.NET, JNCC ArcGIS Extensions or ArcGIS Runtime SDK for Java, which might be similar to ArcGIS Extensibility SDK for Silverlight.