Navit is a car navigation system with routing engine.

Its modular design is capable of using vector maps of various formats for routing and rendering of the displayed map. It’s even possible to use multiple maps at a time.

The GTK+ or SDL user interfaces are designed to work well with touch screen displays. Points of Interest of various formats are displayed on the map.

The current vehicle position is either read from gpsd or directly from NMEA GPS sensors.”

Some people say Navit is also a good choice for pedestrian and bicycle navigation.

http://wiki.openmoko.org/wiki/Navit