S-Dot by Martin Loetzsch is a Common Lisp interface to the 'dot' tool of the GraphViz graphics library. With s-dot, you can specify a graph in an s-expressions syntax and a there are functions to translate these s-expressions into the native syntax of the dot tool.

S-Dot is open source under an Apache style licence.

You may want to check out cl-graphviz and cl-dot.

graph visualization