Pretty cool example of building on and building for Silverlight (Popfly runs on Silverlight and can generate Silverlight code); likely to get a lot more powerful with Silverlight 1.1 and .NET support.
The hosted service, called Popfly and now in alpha testing, gives consumers a visual way to create a Web site or add features, such as mashups, to existing blogs or personal pages. Mashups are Web applications that combine content from more than one source.
Popfly includes a builder tool that allows people to create an application by dragging and dropping block icons onto a design page. These blocks represent tasks or services, such as a widget that displays photos in a slide show, with which a person can build.