Assign more than one containing folder for each of your files and folders.
Tags don’t work anymore in Google Drive. With this app you can assign more than one containing parent folder for each one of your files and folders.
Just select a file or folder, choose "Open with... MULTIFOLDER" from the menu, and you will be able to add an extra folder for that item.
Update on August 2014: solves issues caused by Google's Picker API update.