Clonezilla - Clonezilla is a suite of software that's designed to allow you to back-up and image new hard drives with your data.
SpaceSniffer - SpaceSniffer is a freeWare (donations are welcome) and portable tool application that lets you understand how folders and files are structured on your disks.
Macrium Reflect - Macrium Software - the creators of Macrium Reflect backup, imaging and cloning software.
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
AOMEI Backupper - AOMEI Backupper is a software created to help a person backup, restore, clone, and sync their entire Windows system.
WizTree - WizTree quickly finds the files and folders using the most space on your hard drive. It scans the MFT (Master File Table) instead of crawling the entire disk which makes it very fast.