Cryptomator provides transparent, client-side encryption for your cloud files. It protects your documents from unauthorized access. Cryptomator is free and open source software, so you can rest assured there are no backdoors.
Create vaults in your Dropbox, Google Drive or wherever you like. Assign a passphrase and you're ready to go. Store your sensitive data on the virtual drive provided by Cryptomator. Cryptomator encrypts everything you put into the drive on-the-fly.