Cryptomator

Cryptomator gives you transparent, client-side encryption for files you keep in the cloud on Windows, macOS, and Linux. Your data is encrypted on your device before it syncs, so the cloud provider stores only ciphertext and only you hold the key.

It works with Dropbox, Google Drive, OneDrive, MEGA, pCloud, ownCloud, Nextcloud, and any other service that syncs with a local directory. You unlock a vault with its password and work through a virtual drive as if it were a USB stick; file names are encrypted and the folder structure is obfuscated, and you can keep as many vaults as you like, each with its own password.

Encryption uses AES with a 256-bit key, scrypt key derivation, and authenticated encryption, with transactional, atomic file operations where the filesystem allows.