Graphviz

Graphviz (short for Graph Visualization Software) is a package of open-source tools initiated by AT&T Labs Research for drawing graphs (as in nodes and edges, not as in bar charts) specified in DOT language scripts having the file name extension "gv".

It also provides libraries for software applications to use the tools.

Graphviz is free software licensed under the Eclipse Public License.

Notable applications of Graphviz include:

A red–black tree plotted by Graphviz
Undirected graph showing adjacency of the 48 contiguous United States
A visualization of a JavaScript life cycle made by using Graphviz