I was working on a project and happen to go to the “Start Page” on my Visual Studio and noticed this Microsoft Popfly Alpha under Visual Studio Headlines.
As a technology enthusiasts, I ended up on http://www.popfly.ms and puzzled to see no information on the home page and liked the simple page.
You could Watch the Popfly screencast and it is invite only right now. I have requested for an invitation and waiting for a response. still waiting 
Any how, it appeared to be cool application and looking forward for playing with it soon. It has a Visual studio plugin with which I hope you could write custom apps to upload to Popfly site.
-Cheers