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 Diagram - Professional drawing tool to create Sankey Diagrams.
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.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.