For a PC I would use something like Synctoy, which is essentially a GUI wrapper for Robocopy.
I just googled and it seems like there are some options available. Check out
Mac (OS X) SyncToy alternatives. I have no experience with any of those products, so do some other research before randomly downloading software to your computer.
If you want a more robust option, with email alerts of something has gone wrong, etc, I use Crashplan for rmy backup needs. If you don't backup to their servers it is free, even if you backup to another computer (off-site or on your local network). Then just include the crashplan folder in your other archive.