WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
Avast Cleanup - Next generation tuneup and cleanup for your PC
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.
CleanMyMac X - Clean, protect and speed up your Mac
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.
WinExt Free - Powerful Win utilities: fix registry issues, clean system junk, protect privacy, optimize system, find duplicates, show larger resources, see more info of recently accessed resources, monitor activity, make batch operations, synchronize resources.