QGIS - QGIS is a desktop geographic information system, or GIS.
GPX Editor - Load, modify and save your GPX 1.1 files.
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.
gpx.studio - View, create, edit and combine GPX files online to correct your activity data or design new awesome routes.
SAGA GIS - SAGA - System for Automated Geoscientific Analyses - is a Geographic Information System (GIS)...
GPS Track Editor - GPS Track Editor: Free Windows Application to Make GPS Tracks Better.