For an overview, see: 
Also similar to Satellite Navigation / SatNav, for the benefit of folks who search for that while looking for this page.
What : gpsfeed+, a GPS simulator Where : http://users.hol.gr/~dzach/gpsfeed/index.html Description : gpsfeed+ is a software GPS simulator, a utility that feeds the PC with continuous GPS data as if it were traveling in a car or airplane. NMEA 0183 GPS sentences are sent to the application through a socket (TCP/IP) connection or a UDP message. It also outputs the same NMEA data to a serial port of the PC. Web querying is facilitated by a lightweight http server. Current version: 0.58 Updated : 9-Sep-2005 What: GPSBabel Where: http://sourceforge.net/projects/gpsbabel/ Description: converts waypoint data between over two dozen file formats, including major Palm, PC, and GPS serial formats. Includes a Tcl/Tk GUI. Currently at version 1.1.0 . Updated: 08/2003 Contact: See web site What: Netscape client Tcl Tclets (Caldwell) Where: http://tkfp.sourceforge.net/soarmap (older code) Starkit version: http://www.tcl.tk/starkits/soarmap2.kit (not latest code) Latest version allows circling: http://wiki.tcl.tk/9085 Description: A small and large view of a Soaring Task Map chart. Also the application for gathering GPS data and displaying on a map where the GPS receiver is lcoated is available. Updated: 04/26/2005 Contact: mailto:[email protected] (Alex Caldwell) What: Eagle Where: http://magicnet.net/%7Egcash/ Description: Python/Tk application that interactis with a set of Python classes implementing the NMEA protocol and Lowrance/Eagle protocol - used in some of the Global Positioning System (GPS) hardware. Updated: 12/1999 Contact: mailto:[email protected] (Gene Cash)