I'm working on two GPS applications (on and off) at the moment: one is for managing your stored waypoints and "breadcrumb" trails, and the other is a live monitoring app that tells you where you are, and what's around.
Here's a screenshot of the latter, after about a day's pottering:
It currently runs fullscreen (single tasking). I originally did it becuase I quite fancied the idea of my laptop on the passenger seat running Virtual Acorn, monitoring where I am. However: as I don't actually yet own a copy of VA I have no idea whether it even has serial port support! Maybe time to build that portable A7000+? Or I suppose it might run nicely on an A9.
For test data, I drove round a rural part of Derby with my GPS unit (Garmin eTrex) connected to my laptop running some capture software. My software has the ability to read data from a file instead of the serial port.
... which looks quite interesting, but is possibly a bit pointless ...