http://ppd.develop-help.com/ppd/
http://www.roth.net/perl/packages/
http://www.xray.mpe.mpg.de/~ach/ptk/ppm/
http://theoryx5.uwinnipeg.ca/ppmpackages/
http://dada.perl.it/PPM
http://jenda.krynicky.cz/perl
http://rto.dk/packages/
http://openinteract.sourceforge.net/ppmpackages/
http://ppm.gingerall.cz
http://www.epn.ml.org/~spurkis/Agent/repository 
http://homepage.eircom.net/~jmcnamara/perl