OpenCPN is a free software (GPLv2) project to create a concise chart plotter
and navigation software, for use underway or as a planning tool. OpenCPN is
developed by a team of active sailors using real world conditions for
program testing and refinement.

This plugin creates optimized weather routes using isochrone method and
predictive grib data or averaged gridded Climate data based upon constraint
settings, start and finish information, and boat performance calculated
using boat specs or polar data

Homepage:
http://opencpn.org/ocpn/weather_routing_plugin
