WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.

VisiPics - VisiPics does more than just look for identical files, it goes beyond checksums to look for similar...

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.

dupeGuru - dupeGuru is a tool for finding duplicate files on your computer.

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.

Pixiple - Find images similar in pixel and/or metadata content