You’ll find the list of file synchronization tools broken down into three main categories: open source, freeware, and commercial. Note that even though these file and folder synchronization tools store your data in more than one place, they would not be considered data backup solutions. File synchronization means that when you add, change, or delete a file from one location, the program will perform the same operation at the other location. Hence each copy of the data is the latest copy.
Link: Mashable