It’s called CarotDAV. Download latest portable version here
Then, use FreeFileSync to sync folders locally. For example, I made a subfolder on my Skydrive called Google_Drive and synced all of my Drive documents to that Skydrive folder. You would have to do something similar in the opposite direction too.
Once the desktop utilities have re-synced, you now have access to all of your docs from each cloud.
Note: Skydrive docs can’t open .gdoc yet.
You may have guessed that I have started using Skydrive due to my recent acquisition of a Windows Phone 8 device, a Nokia Lumia 820…
Google Drive Help