Code2Flow - An easy solution to create product flows.
Flowchart.js - Draw SVG flow charts from simple text representations of the diagrams.
asciiflow - Infinite ASCII diagrams, save to Google Drive, resize, freeform draw, and export straight to text/html.
Highcharts - A charting library written in pure JavaScript, offering an easy way of adding interactive charts to your web site or web application
LaTeXDraw - LaTeXDraw is a graphical drawing editor for LaTeX.
Graphviz - Graphviz is open source graph visualization software. It has several main graph layout programs.