There is a wealth of information about the performance of a website available from Google Webmaster Tools. The GWT frontend gives the possibility to manually export this information as several reports in CSV format.
But, to achieve a full integration with an external metrics and monitoring system (for instance, to be able to generate alerts when some conditions are met), a procedure to perform automatically the download of this information is required.
This post reviews a free and open source utility named GWTData that implements this functionality.