Files with the extension .GBF are data files created and used by 'Gtrek' a data logging system that utilizes a small physical GPS tracking unit to log a users movements.

The .GBF data file contains a detailed geographical record of a users position at any given time, plus other route information such as how far they traveled, and how fast, etc. This information can then be analyzed with the accompanying software, as well as within 'Google Earth/Maps'.