Kopia

Kopia is a free, open-source backup tool that refuses to lock your data into anyone's cloud. It encrypts everything on your own machine first, then stores it wherever you point it: an external drive, a NAS, Amazon S3 or any S3-compatible service, Backblaze B2, Google Cloud Storage, Azure Blob, WebDAV, SFTP, and Dropbox, OneDrive or Google Drive through rclone. You can even keep several repositories at once, with different machines backing up to different providers.

The project comes in two flavors that share the same repository format. The command-line tool is a single small binary built for scripting, cron jobs and servers. KopiaUI wraps the same engine in a desktop app for Windows, macOS and Linux, with snapshot browsing, scheduling and policy management built in. Pick whichever fits; switching later costs nothing.

Under the hood, Kopia does the three things that make backup storage cheap. Content-defined deduplication stores identical chunks only once, even across machines sharing a repository. Compression (zstd, s2 or pgzip, your call) shrinks the rest. And snapshots are incremental, so after the first run only what changed gets uploaded. In a space where backup tools love to charge subscriptions for exactly this, getting it free under the Apache-2.0 license feels almost suspicious.

Security is not an afterthought here. Backups are end-to-end encrypted with AES-256 or ChaCha20, with keys derived from a password that never leaves your device. Your storage provider sees ciphertext and nothing else. Reed-Solomon error correction adds protection against bit rot and flaky hardware, which is the kind of detail you only appreciate the day a restore actually works.

Restoring is flexible: mount any snapshot as a local drive and drag files out, restore a full tree to a folder, or grab a single file from an older version. Retention policies let you decide how many hourly, daily, weekly and yearly snapshots to keep, applied globally or per directory, so a laptop and a server can follow different rules inside the same repository.

A few honest caveats. Kopia is still pre-1.0 software, and the GUI covers the common cases while advanced options often send you back to the CLI. There is no official mobile app, and backing up to a friend's machine means running a repository server yourself. New users coming from one-click backup tools will need an evening with the documentation.

For a community-maintained project, the momentum is real: over 14,000 GitHub stars and millions of downloads across releases, with version 0.23.1 released in June 2026. If you want backups you fully control, encrypted by default, stored wherever you like, Kopia is one of the strongest free options available today.