Here is a simple gps and nmea 0183 port monitor I wrote in python called nmeamon. Built for Linux, it's a tool that allows you to view raw incoming data from most gps and nmea 0183 devices via serial port, bluetooth, or the gpsd daemon.

Source code for nmeamon is here: nmeamon_source

This installer package is built for Ubuntu Linux.
Download nmeamon-0.3.deb

After installing launch from menu:
Applications --> Accessories --> NmeaMon

NmeaMon will scan for serial, usb-serial, bluetooth serial and gpsd daemon and make them available to view in it's terminal window. You can also specify serial devices manually by typing in the NMEA Device drop-down box. Nmeamon will only open gpsd on localhost and the default port 2947.