This work could not have been completed without the generous help of numerous people.  In
alphabetical order, hopefully including all who have helped:

From the Graphviz developers email list
  John Ellson	
  Emden R. Gansner
  Stephen North
  Gordon Smith

Help with the R package, extensive testing and building
  Dan Tenenbaum

Help with porting to 64 bit Windows, and for making 64 bit Windows binaries of Graphviz available.
  Brian D Ripley

Testing and bug reporting
  Claus Bendtsen
  Henrik Bengtsson
  Thomas Cokelaer
  Laurent Gautier
  Anand Gavai
  Klaus K. Holst
  Mike Jiang
  Mikko Korpela
  David Meyer
  Roger D Peng
  Adi Tarca
  Jitao David Zhang