Cryptomator provides transparent, client-side encryption for the cloud (and locally, too).

The program creates an AES-encrypted file in your Dropbox folder, Google Drive, or whatever other location you like. Just specify the file name, location and a passphrase, and you're done.

Once the vault is set up, Cryptomator mounts it as a virtual drive on your computer.

Save any documents to that drive, and they're automatically encrypted, then uploaded to the cloud (if this is a cloud storage folder).

When you're finished, lock the vault, the virtual drive disappears, and no-one will even know it's there.

Cryptomator is available on multiple platforms, allowing access to your data from almost anywhere, but keep in mind that the iOS app is a commercial product ($4.99).

What's new in 1.4.12 (see changelog for more)?

- Added "save password" capability to Linux systems with GNOME keyring or another keychain via Secret Service API (#422), kudos to @purejava and @swiesend ??
- Added "custom mount flags" option to Dokany/FUSE (#802), use at your own risk!
- Added launcher scripts to buildkit for using Cryptomator via JAR (#843)

Verdict

A simple way to secure your cloud files, and access them from just about anywhere.