Time Machine tool that lets you dig through your backed up files' history.
With a little external hard drive, Apple's Time Machine application will save your bacon in the event of a hard disk failure. And if that external drive is big enough and configured it properly, you can also go back and resurrect work that you had trashed or overwritten weeks or months ago. But if you've ever done that, you know Apple didn't make it very convenient, especially if you want to, say, look at the history on one particular file.
Manage partitions of Mac OS X.
Optimize performance of a slow Mac hard drive.
Find and remove duplicate on your Mac