Connect to GPS receiver, and analyse the connection
gpsd is a GPS service daemon for Linux, OpenBSD and Mac OS X. There's also a Windows version. It can connect to GPS receivers via serial, USB port, Bluetooth, or via another gpsd through the network (TCP/IP connection). Many mapping and map viewing application use it, for example FoxtrotGPS, Marble, Merkaartor, QLandkarteGT, TangoGPS and Viking. Also some navigation applications like GpsDrive, Gosmore, Navit and ShareNav can use it to show current position on map on a laptop computer.
gpsd shipped with some client programs, which can use to monitor GPS position, and check the connection with device.
xgps is a simple test client for gpsd with an X interface. It displays current GPS position/time/velocity information and (for GPSes that support the feature) the locations of accessible satellites.
xgpsspeed is a speedometer that uses position information from the GPS.
cgps is a client resembling xgps, but without the pictorial satellite display and able to run on a serial terminal or terminal emulator.