Digging around a little bit in the world of carputers following our recent post on the Subaru carputer, I came across Roadnav, a cross platform, open source GPS mapping program from Richard Lynch. One thing that makes this project different from many commercial solutions is that it uses free US mapping data from "the US Census Bureau and the USGS." It then renders the maps from that government data. I believe most commercial mapping data is supplied by Navteq, whose trademark you are probably used to seeing at the bottom of Google Maps. Roadnav is a bit rough around the edges, but given the limited number of GPS navigation solutions for the Mac it's certainly worth checking out.