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Pro Shared folder spacing control
Copy.com allows users to control how the shared folder can use others user account space, eg: if the main user account has 20GB of free space and wants to share the folder to other user, the shared folder can be limited to 5GB instead of fully occupying the other user's free space.
Copy.com is available on Windows, OS X, iOS, Android, Linux (including Raspberry Pi) and has a web app.
Pro Automatic photo backup
Copy.com allows users to automatically backup photos taken from the device through the feature called "Photocopy".
Pro 20GB for free-tiers
Free-tier of Copy.com allows for up to 20GB through the referral service (original is 15GB).
Con It's shutting down
Copy is shutting down in early 2016