Viking is a free/open source program to manage GPS data.
You can import, export and plot tracks, routes and waypoints, show various OpenStreetMap, Bing Aerial and other maps in it, create maps using Mapnik (http://www.mapnik.org).
Download Wikipedia points, OSM Traces or Your Personal OSM Traces for an area on the map.
Make new tracks, routes and waypoints and geotag images.
See real-time GPS position (but not on Windows as no GPSD support on this platform).
The main wiki is HERE. This used to be the MediaWiki wiki but has been imported into Allura since Sourceforge dropped hosting of the MediaWiki installation in June 2014 :(
DEM Layer of the UK + tracklogs of a weeks long Road Cycle
Cycle Map (OSM) with many MTB Tracks in the south of the UK
Trackpoint Edit Dialog. Mapquest. Wales Various Tracks.
Geotagged Images (Size 128 + Alpha) + Stamen Watercolour Map