GPSylon is able to show maps downloaded from the expedia map servers. It may connect to a GPS device and track your position on the maps. At the moment, it is able to read gpsdata in the NMEA standard from a serial gps device, a file or a gps daemon across a network (available at the gpsd project page).
The main feature is the display of various maps. GPSylon allows the user to navigate around like in a digital atlas. It shows maps of different scales, so missing maps of one scale do not result in a black screen, but show the next larger scale. See the screenshot section for an image.
It uses the open source library openmap for various cartographic things.