Springgraph is a GPL'd program for reading "dot" files (describing a graph).
It is similar to the "neato" program, except neato is not Free software.

See http://www.chaosreigns.com/code/springgraph/

This particular version of springgraph has been hacked up by me (John
McPherson) to generate Postscript output.

Sample usage:
gpg --list-sigs --keyring xyz.gpg | ./sig2dot.pl | 
  ./springgraph.pl --format ps > xyz.ps


springgraph.pl:

Reads a .dot file and generates an image (defaults to standard out).


sig2dot.pl:

Reads gpg signature data on standard input, and prints a dot file to
standard output.
Keys are given different colours, depending on the number of "in-links" and
"out-links".

make_pdf.pl:
Example program that calls the above scripts for your default gpg keyring,
and then converts the output postscript file into a PDF file.