Does anybody have any suggestions for such an animal? Collaborative would be even better, but any diagram-generator with the correct input/ output/ processing/ store symbols and arrows capabilities would do fine. After googling for it, I'm surprised there are no obvious, standing-out examples of such interactive tools online [sample free trial PC desktop app: http://www.smartdraw.com/specials/ppc/softdesign.htm?id=173461]

Is this something?

http://www.yworks.com/en/products_yed_about.html

Not a flow state diagram site, but for sequence diagrams ... http://www.websequencediagrams.com/