Cryptomator encrypts your files before they reach cloud storage, so only you hold the key. It's a free, open-source tool for anyone who keeps personal files in Dropbox, iCloud, Google Drive or similar services.

Key features:

Create a password-protected vault inside any cloud folder, with no registration or key setup.
Unlock a vault to get a virtual drive that encrypts whatever you move into it.
Encrypt both file contents and file names with AES-256.
Create unlimited vaults that work with any cloud storage.
Rely on open-source code that's checked in independent security audits.
Share vaults with a team through Cryptomator Hub, with zero-knowledge key management.

The desktop app is free for personal use; Dark Mode on desktop is an optional one-time upgrade from €29.99 (€19.99 during a sale), and the iOS and Android apps are sold separately. Cryptomator Hub Standard for teams costs $12 per seat per month.