Magellan Meridian
Here it is, the amalgamate of an old Atari hack and a new Perl/tk hack. Its purpose is to let me see the goings on inside my Magellan Meridian GPS.
In the green field the different screens from the Meridian are displayed. Below these the NMEA data from the GPS scrolls by. There is room at the same time for all the six different sentences transmitted by the GPS. The only sentences that are decoded are: VTG, RMB and GGA, these are enough to compute the contents of the screens. The only thing missing is the name of the waypoint, which in this case isn't "1".