Sankey Diagram (csaladen) - Sankey Diagram Generator
LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
Sankey Flow Show - Online flowchart maker: Sankey Flow Show is a modern online web application running in your browser.
draw.io - Online diagramming application
SankeyMATIC - There are no tools to install. There is no code to write. You do not have to sign up for anything. Just enter your data, customize the diagram to your liking, and download a finished product.
yEd - yEd is a free desktop application to quickly create, import, edit, and automatically arrange diagrams. It runs on Windows, Mac OS X, and Unix/Linux.