Any Hard drive Mirroring or Software Raid or Sync tools on the Mac that are free?
The Apple provided Disk Utility (and diskutil shell command) will allow you full RAID control over internal and external drives. You do have to erase the drives to add the RAID capability, but then you can join those drives into RAID. That is the only potential drawback to implementing RAID storage on the Mac.

Drive spanning, JBOD, striping and mirroring are all possible with Mac OS X software RAID.

Lion brings the concept of physical and logical volumes to the OS, but RAID on Snow Leopard is also very fully functional.

If you brake a mirrored RAID set - the drives are valid when connected to the same mac and portable to any other mac. You are not locked into a proprietary standard and don't need any additional software for any of this functionality.

rsync and ditto are free sync tools - very scriptable, powerful, and free.