If you want to create a graph and don’t want to use a commercial program, you’re looking for yEd. yEd is a desktop application for Windows, Linux or Mac. You can also download a Java version of the application.
With yEd creating diagrams is easy. There are several pre-defined palettes to chose from, icons, labels, figures and more. With these tools it’s possible to create great looking diagrams. There’s a gallery on the site, just have a look at it.
It’s possible to import SVG graphics to use with your diagrams, so what kind of diagram you can create sounds limitless. Just don’t try to import the micropores diagram, that one is a bit big.