GPX Editor is a free, open source GPX file editor for Windows.
GPS Track Editor
GPS Track Editor, as the name suggests, is a free software to edit GPX files containing tracks.
Extra POI Editor
It has a tiled interface which shows points, preview, map, and more information.
Viking
Viking is another free, open source GPX editor software for Windows. You can edit GPX files by modifying routes, waypoints, and tracks.
Garmin BaseCamp
Garmin BaseCamp is quite a popular GIS software for Windows and Mac. You can also use it to edit GPX files.
JGPSTrackEdit
JGPSTrackEdit is a free, portable GPX editor for Windows. It lets you edit Garmin GPX Track files. For editing, it supports more file formats including KML, ASC, etc.
GpsPrune
GpsPrune is another alternative to software to edit GPX files. As you open a GPX file, its waypoints are listed at left panel.
3D Route Builder
3D Route Builder is the next GPX editor for Windows. To start editing a GPX file, enable edit mode from Route menu.
ITN Converter
ITN Converter is basically a route converter and planner software for Windows. This can also be used as a GPX editor.
To know more about these software click on the icon below.