Never heard of it. Because it is silverlight, never would have been able to run it. Sounds like it did a lot less according to http://blog.jonudell.net/2008/02/14/popfly-and-pipes/

Lemme guess, you worked on it?

Of course! No other reason to mention a Microsoft project that's been dead for four years otherwise :)

Hah. Well, you shipped something. I have to imagine that's incredibly hard.