QGIS - QGIS is a desktop geographic information system, or GIS.
GRASS GIS - GRASS GIS is a free Geographic Information System (GIS) software used for geospatial data management and analysis, image processing, graphics/maps production, spatial modeling, and visualization.
SAGA GIS - SAGA - System for Automated Geoscientific Analyses - is a Geographic Information System (GIS)...
GeoDa - GeoDa is a GIS-based software that provides a user-friendly and graphical interface to methods of exploratory spatial data analysis to conduct visualization, spatial analysis, spatial modeling, and spatial auto-correction.
Whitebox GAT - Whitebox GAT is an open-source, cross-platform GIS-based software package that is intended for advanced geospatial analysis and data visualization in research and education.
GPX Editor - Load, modify and save your GPX 1.1 files.