In MacOS 9, there was a control panel that synced 2 folder, being a student I used it to sync a floppy (Yes, I was still using floppy disks) to a folder on my computer, because floppies were easily lost or damaged.
Now that I am in college, I use a 1 GB USB flash drive to carry all my data on. I am currently using a free utility to sync my data, but it is painfully slow when I have only change 1 or 2 files. I do not want to pay for a application to sync.