You can multi-select objects in diagram by using Ctrl + Mouse Click. As for the context menu appearing on right mouse click - we haven't a template or style for that, but you can use the RadContextMenu
and diagram commands
to achieve the described behavior.
I'm attaching a sample project that demonstrates this approach and hope that this will give you an idea how to further customize the diagram according to your requirements. Please feel free to ask if you need any other assistance.
Check out Telerik Analytics, the service which allows developers to discover app usage patterns, analyze user data, log exceptions, solve problems and profile application performance at run time. Watch the videos
and start improving your app based on facts, not hunches.