FreeFileSync is a desktop tool for comparing and synchronising folders and for file-based backup. It transfers only the data needed to bring a source and a target folder into line, and it offers two-way, mirror and update modes, a database file to track changes, parallel file copying, and support for FTP, FTPS, SFTP and Google Drive. It runs on Windows, macOS and Linux and is installed locally, with no vendor-operated cloud service involved.
FreeFileSync is published by FreeFileSync.org, whose company details give an address in Hamburg, Germany; the project lead and copyright holder is Zenju. The source code is released under GPLv3 with an additional condition: the standard and donation editions are for private use only, and businesses and public bodies need the paid Business Edition. An independent review therefore rates its openness as having issues. Because the software runs on your own systems, your data stays wherever you choose to store it, which lets a European organisation keep synchronised files within the EU.