Setting Up an RSnapshot Backup System
RSnapshot is a UNIX backup system based on the underlying Rsync utility and protocol. OSTechNix looks at How to Implement a UNIX Backups System Using RSnapshot. This is a powerful, free, robust, open source backup system that is very capable, but extremely limited if you choose to move beyond the UNIX world and does require a bit of expertise to implement properly.
I've used rsnapshot a good bit and it's a really nice tool for simple backups.