The best open source alternative to NordLocker is Cryptomator. If that doesn't suit you, we've compiled a ranked list of other open source NordLocker alternatives to help you find a suitable replacement.
NordLocker alternatives are mainly Encrypted Storage Tools. Browse these if you want a narrower list of alternatives or looking for a specific functionality of NordLocker.
Encrypts files and filenames locally before they reach Dropbox, Google Drive, OneDrive, or any other cloud, so only you hold the key.

Cryptomator sits between your files and your cloud storage, encrypting everything locally before it ever leaves your device. Most cloud providers either encrypt only during transit or hold the decryption keys themselves, which means they (and anyone who compels them) can read your data. Cryptomator removes that dependency entirely.
Setup is intentionally minimal. You create a vault, assign a password, and Cryptomator mounts it as a virtual drive on your system. Anything you drag into that drive is encrypted automatically. No key management ceremony, no account registration, no configuration files to maintain.
How it protects your data:
The desktop version is free. Mobile apps carry a small one-time fee. The code is fully open source and has been independently audited by security researchers, with automated testing and public code coverage metrics.
For teams, Cryptomator Hub adds centralized access management. Members unlock shared vaults with their own accounts rather than a shared password, and it integrates with existing identity providers. This makes it practical for businesses that need GDPR-compliant cloud collaboration without routing files through a third-party service.
If you're looking at alternatives to Boxcryptor or Tresorit, Cryptomator covers the core use case (cloud encryption you control) at no cost for desktop users. For self-hosted encrypted storage, tools like Peergos or Hoodik take a different approach worth comparing.