Duplicati

A free backup client that encrypts your files locally before they ever leave the machine and then sends only changed blocks to the destination you choose. It speaks to a long list of targets, from S3, Azure and Backblaze B2 through Google Drive, OneDrive and Dropbox to WebDAV, SFTP and local network shares, with a scheduler, filtering rules, retention policies and a web interface for managing jobs.

It fits mixed estates where Windows and Linux desktops and servers back up to cloud or on-premises storage without a dedicated appliance.

Pointing it at storage you run keeps the backup copies and encryption keys under your control, avoids fees tied to machine counts or storage volume, and restores stay a matter of running the client against your own destination.