WatchDISK Disk Space Tracker 

WatchDISK provides the information you need to: Find out why free disk space has suddenly dropped, Project future storage needs, Justify additional storage capacity investments to management. Includes automated scans and low disk space warnings.
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diskSpace Explorer Home Edition 

diskSpace Explorer 3 Home Edition is a software tool for managing your hard disk space, and ensuring that you are making the most of the space you have. The program shows a graphical display of your hard disk and can help you free up valuable space.
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