The mincrosssings is a GNU GPL free sugiyama barycenter layout
algorithm in C with tools and documentation available, ready to
create your own GPL free graph layout program.
and a local backup is here in mincrossings.tar.gz
documentation to see the c source is here in these doxygen pages
In fact only need to add a parser and drawing part and few more
graph routines to it to make a tool.
Other graph software from matthias stallman is here in stallman-software.tar.gz
and better explained what it is about here
And this is used for chip design with such kind of graph data: