This is what many have been waiting for, I think. The first Sankey app for iOS.
I have not tested it myself, since I don’t use iOS. But in the video on the Squishlogic website it looks fancy and moving around the nodes seems smooth. In the video they don’t show how arrows are drawn and flow quantitites are entered, but maybe Steve (who pointed out that new tool me) will comment.
Added to the Sankey diagram software list.