Though am planning to update soon...
(I have no idea if you're doing web or application development.)
Since i first used yahoo pipes, years ago, i have a project in mind where i could use exactly this functionality.
I was always to lazy to give it a shot on my own, but i think now would be the right time. I'll keep you updated.
It is a great way to make drag-n-drop widgets that work for pretty much any browser. Simon has done an awesome job with this.
Happy to put up a link when shipped so you can see JsPlumb in action.