Roadnav is open-source navigation software meant to be run on an in-car computer connected to a GPS; it runs on Windows, Mac OS X and Linux. “Roadnav can obtain a car’s present location from a GPS unit, plot street maps of the area, and provide verbal turn by turn directions to any location in the USA. Roadnav uses the free TIGER/Line files from the US Census Bureau to build the maps, along with the GNIS state and topical gazetteer data from the USGS to identify locations.” At version 0.16 and looks a little rough around the edges. Via The Unofficial Apple Weblog.