Dropbox - Online Sync and File Sharing
GoodSync - GoodSync provides highly reliable file backup and synchronization for both individuals and businesses.
Google Drive - Access and sync your files anywhere
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.
Nextcloud - With Nextcloud enterprises host their own secure cloud solution for storage, collaboration & communication from any device, anywhere.
FreeFileSync - FreeFileSync is a free open source data backup software that helps you synchronize files and folders on Windows, Linux and macOS.