From Tamer Louis:
Google Earth Voyager (GEV) is a program for automatically building a Google Earth cache file for a specified geographic area. GEV does this by controlling Google Earth, making it systematically scan over the area you want to cache. Google Earth caches what you see on the screen. This means that the size, resolution and selected layers is saved in a file on your hard disk. The next time you look at the same area, Google Earth will first check to see if it can retrieve the data from the cache in order to save time and bandwidth. This also means you can use Google Earth offline as long as the area you want to look at is available in the cache. You can scan an area into the cache by using your mouse to manually move the viewpoint in Google Earth over the area. Unfortunately this is not very practical when you want to scan larger areas with a detailed zoom-level. This is where GEV comes in: it can tell Google Earth to move the screen viewpoint around in a systematic fashion.