Navit

Navit is a car navigation system with routing engine.
It's 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.
The routing engine not only calculates an optimal route to your destination, but also generates directions and even speaks to you using speechd.