The free online srvice which is still at its Alpha stage provides a way to construct mashups by combining various web 2.0 applications. The application users microsoft's Silverlight browser plugin which is now in beta. In order to use Popfly Alpha, you have to sent an invitation request. For more info visit webware blog post on popfly.
Below are videos showing what popfly is,its features and how to use the application.
To checkout my embedded mashup click here.