Graphviz is open source graph visualization software.  It has several
main graph layout programs.  It also has web and interactive graphical
interfaces, and auxiliary tools, libraries, and language bindings.

Graph visualization is a way of representing structural information as
diagrams of abstract graphs and networks.  Automatic graph drawing has
many important applications in software engineering, database and web
design, networking, and in visual interfaces for many other domains.

gts and DevIL are autodetected optional dependencies.
ocaml is an optional dependency, if you want OCaml bindings.