Cryptomator is a free and open source client-side encryption solution for your cloud files, available for Linux, Windows and Mac OS X, as well as iOS. An Android app is currently under development.
Cryptomator is advertised as being especially developed to encrypt your cloud files from services such as Dropbox, Google Drive, Mega and other cloud storage services that synchronize with a local directory.
Since the encryption is done on the client side, it means that no unencrypted data is shared with any online service.
Furthermore, you can use Cryptomator to create as many vaults as you want, each having individual passwords.
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