Any Hard drive Mirroring or Software Raid or Sync tools on the Mac that are free? I am trying to mirror a hard drive that is 3TB on the PC using SyncToy from Microsoft's PowerToys  (as a backup method).  But Mac is usually better for indexing and content searching, but is there either something similar to SyncToy on the Mac, or any Software RAID or Sync tools on the Mac that are free?

I don't want to use a hardware RAID drive because (1) it is expensive and (2) if the RAID controller becomes bad, then I can't access either drive (unless if I remove the case and somehow connect the drive by itself, I think?  -- which is not as simple as two independent hard drives, because then if one drive fails, there is still another fully working drive right there to be used immediately)  thanks.
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.