Dropbox - Online Sync and File Sharing
Filestash - Filestash is a modern client for FTP, SFTP, S3, WebDAV, Minio,...
Google Drive - Access and sync your files anywhere
Syncany - Syncany is an open-source cloud storage and filesharing application.
Nextcloud - With Nextcloud enterprises host their own secure cloud solution for storage, collaboration & communication from any device, anywhere.
FTPSync.pl - FTPSync.pl is a PERL skript to synchronize a local directory tree and a remote FTP directory tree.