A downloadable tool for Windows
SimpleSync is a lightweight file synchronization tool I created for myself to synchronize my files to a back-up location.
The program does not install, is fully portable, and is less than 500kb in size.
SimpleSync offers a variety of options for how you want to synchronize two folders, remembering the previous settings as well as offering a user-configurable default set-up. Additionally the program can be called using the command line, so you can use a batch file to run a routine back-up (my preferred sync method) or use some other automation program.
More information on the usage, settings, and command line options included in the ReadMe file.
Being perhaps overly cautious I will say that you use the program at your own risk and I accept no responsibility for lost files or incorrect use. However I have tested it fairly comprehensively, this program was created to fulfill my own needs and have been using it for years now without any issues.
Icons by Mark James (http://www.famfamfam.com/lab/icons/silk/) used under the creative commons attribution licence.