#5 Google Drive

Google Drive is a file storage and synchronization service by Google. It is now the home of Google Docs, a suite of productivity applications that offer collaborative editing on documents, spreadsheets, presentations, and more.

Google Drive gives all users 5 GB of cloud storage to start with. A user can get additional storage, which is shared between Picasa and Google Drive, from 25 GB up to 16 TB through a paid monthly subscription plan ($2.49 US per month for 25 GB).

Gmail is well integrated with Google Drive. Just sign in to your email account and click 'Drive' on the top bar. Select the files you want to share (multiples possible), add email addresses and click send.

Also, like Dropbox, it integrates with Windows and Mac file systems, Chrome OS, Android, and Apple's iOS.

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