freebsd-ports/ports-mgmt/pkg-graph/pkg-descr

pkg-graph is a command-line utility to generate a dependency graph in
DOT syntax (for use with graphviz and others) to represent the
dependency tree of installed packages. It can be used to visually
analyze the package dependency chain and understand why certain packages
are pulled in.

WWW: https://github.com/neosmart/pkg-graph