A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robert VanderPol II
Date: 2015 Oct 23, 00:09 -0700
There are other free alternatives but this is the one I am familar with.
Free charts can be had from the US (US waters only), Brazil and New Zealand (NZ and a bunch of Pacific Islands) and a few others. Elsewhere you will need to pony up for the charts.
To make this work with a laptop you will need a GPS dongle.