Windows User
GMail Drive is a Shell Namespace Extension that creates a virtual filesystem around your Google GMail account, allowing you to use GMail as a storage medium.

GMail Drive creates a virtual filesystem on top of your Google GMail account and enables you to save and retrieve files stored on your GMail account directly from inside Windows Explorer. GMail Drive literally adds a new drive to your computer under the My Computer folder, where you can create new folders, copy and drag'n'drop files to.
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Linux User
GmailFS provides a mountable Linux filesystem which uses your Gmail account as its storage medium. GmailFS is a Python application and uses the FUSE userland filesystem infrastructure to help provide the filesystem, and libgmail to communicate with Gmail.

GmailFS supports most file operations such as read, write, open, close, stat, symlink, link, unlink, truncate and rename. This means that you can use all your favourite unix command line tools to operate on files stored on Gmail (e.g. cp, ls, mv, rm, ln, grep etc. etc.).
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