Viking is a free/open source program to manage GPS data. You can import, plot and create tracks, routes and waypoints, show OSM, Terraserver, Bing Aerial and other maps, geotag images, see real-time GPS position, get geocaches, control items, etc. It is written in C & the GTK+2 toolkit.
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 :(