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

Avast Cleanup - Next generation tuneup and cleanup for your PC

TreeSize - TreeSize tells you where precious disk space has gone to.

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.