The worldwide geocoding webservice is totally FREE and allow to find GPS coordinate and other informations for a given text (address, street name, city, zip,...) in 243 countries, via a REST webservice.
It uses (free) data from OpenstreetMap that are imported into a local database.
Gisgraphy doesn't use Google Maps geocoder, it do it by itself, it only use Google Maps to display the result of the search.
You can see an example of use bellow. You can find documentation on how to use the XML API of the webservice and see how to download and install Gisgraphy.