Google Earth is being used for everything from plotting demographic data to video production, and there are a number of add-on apps available.
SketchUp is a free utility that allows you to create 3D models for Google Earth. The program is basically a CAD tool, and although it offers Google Earth support, it can be used to create other types of drawings and 3D models as well. Perhaps one of the most useful features is that you can download 3D buildings and other objects from an online library. Once you do, you can use the model in its existing form or you can use the drawing tools to modify it.
RoboGEO is a utility for geo tagging image files. Geotagging can be based on Google Earth, an NMEA file, a waypoint file, a track file, or any number of other sources. It is also possible to manually enter GPS information. The geo tagging data is added directly to the file's meta data and you are also given the opportunity to add a title to the image.
A personal license for RoboGEO sells for $79.99, but a free trial is available for download.
3. Google Earth KMZ or KML to GPS Converter
Google Earth KMZ or KML to GPS Converter is a tool that you can use to convert Google Earth data to a GPS compatible format (a .GPS file). The utility allows you to import the KMZ or KML files that you create with Google Earth and then use them to build waypoints, routes, or tracks. You can import KMZ files in any order and arrange the locations in the preferred order before exporting them.
Google Earth KMZ or KML to GPS Converter sells for $20, but you can perform ten free trial conversions.
4. Google Earth API
The Google Earth API is a free tool for building onto Google Earth. One of the best parts of the API is the Google Earth Plug-in. You can use this plug in to display Google Earth (and any custom features) within a Web browser.
The plug in seems to have problems with Internet Explorer 10, but works fine in Internet Explorer 10 Compatibility View. It is also worth noting that Google provides numerous code samples that you can use to add Google Earth imagery to your Web site.
5. Cache for Google Earth
Cache for Google Earth is a utility that allows Google Earth to be used while working offline. Google Earth does offer a built in cache that can be used for offline use, but the cache's contents can be a little bit unpredictable to say the least. This utility allows you to save the cache contents while they are in a predictable state and then retrieve them for later use.
This utility will likely be useful to those who use Google Earth outside of their office. For example, I built a drone that can be GPS controlled. The drone's position is tracked through a specialized interface that uses Google Earth maps. The problem is that when I am in the field, there is often no Wi-Fi link available for downloading Google Earth imagery. For this type of application, Cache for Google Earth could potentially be used to make the imagery portable.
Cache for Google Earth sells for $19.00, but a free trial is available for download.