DiskCheckup measures the performance and 'health' of your S.M.A.R.T. enabled hard disk drive. It compares current hard disk attributes to values determined by the manufacturer of the HDD. It can track changes to the attributes over time and make a extrapolated 'prediction' as to the failure date of the HDD. It can be command line driven and can be configured to send alerts by email. Free for personal use, $US 15.00 for commercial use.