Viking is a free/open source program to manage GPS data
GPS log file viewer and analyzer
Simple GPS tracking server
Open source system for GPS tracking devices
NMEA 0183 library for Java
Plugins for OpenCPN
GPS mapping and management software
Open Source Marine Chart Plotting Program
This is a port of LibRTK on C#, and into a small c/c++ library.
A tile-based map viewer with support for GPX files.
A gui for linux users of miniHomer, a GPS tracker
a free and open map of wireless communicating objects
GPSBabel converts and transfers data like waypoints, tracks & routes.