MirrorBackup.net - Mirror Backup protects from data loss by continuously monitoring files and folders, and backing them up to the cloud or a local drive when they change.

FreeFileSync - FreeFileSync is a free open source data backup software that helps you synchronize files and folders on Windows, Linux and macOS.

AnyBackup - AnyBackup is designed to keep two pools of volumes in sync with one another.

Qtd Sync - A graphical interface for the Rsync engine that will synchronise files between two computers either...

@MAX SyncUp - An advanced tool for Windows to compare and synchronize files and secure data backup either locally or to FTP/SFTP, Google Drive, and more.

rsync - rsync is a file transfer program for Unix systems. rsync uses the "rsync algorithm" which provides a very fast method for bringing remote files into sync.