Allway Sync uses innovative synchronization algorithms to synchronize your data between desktop PCs, laptops, USB drives and more. Allway Sync combines bulletproof reliability with an extremely easy-to-use interface.

From author's site:

Cobian Backup is a multi-threaded program that can be used to schedule and backup your files and directories from their original location to other directories/drives in the same computer or other computer in your network. FTP backup is also supported in both directions (download and upload).

From author's site:

SyncBack is our freeware program that helps you easily backup and synchronize your files to: the same drive; a different drive or medium (CDRW, CompactFlash, etc); an FTP server; a Network; or a Zip archive.