GDocBackup
GDocBackup stopped working on April 20, 2015 when Google deprecated and stopped the APIs used by the tool.
Fell free to contact me if you need more information.
UPDATE
If you are using Google Workspace, formerly G Suite and Google Apps - and you’re looking for a solution like GDocBackup, take a look at DriveExport. It’s very similar to GDocBackup. It supports G Suite accounts, exporting all company files from users Drive respositories and Team Drives folders. (Note: it does not work with personal/consumer GMail accounts.)
** FROM THE OLD WEB SITE **
Google Docs backup utility
Overview
GDocBackup is simple utility to backup (export) all your documents from Google Docs to local disk. It’s open source, freeware and licensed under the Apache License Version 2.0 It does a simple backup: for each document in Google Docs, it downloads the document if the document is not present on the local disk or if it has a different date. GDocBackup runs on Windows (tested on XP, Vista and 7), Linux (tested on Ubuntu 8.10 and OpenSuse 11.1) and Mac (tested on OS X 10.5.6). Required .NET or Mono.
IMPORTANT: GDocBackup uses the official Google Data APIs (.NET version). So the quality, accuracy and correctness of the exported files is out of the control of GDocBackup. If you encounter problems in the exported documents (i.e. the exported doc is not similar to the original on Google Docs), contact Google Docs support forum.