FTP Synchronizer - Secure and high performance FTP File Sync product
FTPbox - FTPbox is an open-source application that allows you to synchronize your files to your own host...
FreeFileSync - FreeFileSync is a free open source data backup software that helps you synchronize files and folders on Windows, Linux and macOS.
Dropbox - Online Sync and File Sharing
Syncany - Syncany is an open-source cloud storage and filesharing application.
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.