It draws a pretty picture of your installed packages.
To try it yourself, get the code. It will generate an SVG. If Inkscape or imagemagick is installed it will also render a PNG. It might seem a little slow, but it's many times faster than Graphviz.
Right now Arch is the only supported distro, but writing new loaders is pretty easy.
Stuff supported from the command line:
Want to make only an SVG, no PNG? pacgraph --svg
Custom colors? Each of these takes one color, such as
Font size can be set with pacgraph -p 10 100 where the first number is the smallest point size, and the second is the largest.
Distro is chosen through -m / --mode. Current supported options are arch (which graphs your installed packages) and arch-repo (which graphs every offical package in the repositories). Do not be alarmed if arch-repo takes a few minutes.