How can I generate rectangle style edges instead of curves in GraphViz?
This feature is called "orthogonal edge routing" and is available in Graphviz versions from September 28, 2010 and newer. Use "graph [splines=ortho]"; see the Graphviz documentation.
digraph Orthogonal { graph [label="Orthogonal edges", splines=ortho, nodesep=0.8] node [shape=box] a->{b c} b->{d e} c->{f g}}