Google Drive – Google drive offers you 5GB of free online storage, you can sync your PC documents to keep them always available to you even without internet connection. Google drive is just an extension of Google docs that you are using with your gmail earlier. But using drive you can now sync your files between your PC/Smartphone to cloud storage easily .
In google drive also you can view & edit your word/excel/ppt files but it is not your traditional MS office environment it is bit of some different than your MS office.
For more info see this link – https://drive.google.com/start#home