Sankey diagrams are a specific type of flow diagram, in which the width of the arrows is shown proportionally to the flow quantity. They are typically used to visualize energy or material or cost transfers between processes. However, they can also be used to visualize cash flows within a business or business unit.
While a Sankey diagram is simple to understand, they are laborious to create and maintain.
To make things easier, I created a custom Sankey diagram generator for my web development business (Bowtie Websites). It takes data from a Google Docs Spreadsheet and extracts specific data from the worksheets inside of it. Thus, to update the diagram, I simply need to update my spreadsheet and reload the diagram.
This project draws heavily on the Data Driven Documents project (http://d3js.org/) and makes use of the Zend Google Docs libraries.