Avast Cleanup - Next generation tuneup and cleanup for your PC
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
CleanMyMac X - Clean, protect and speed up your Mac
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.
CCleaner - CCleaner cleans, speeds up and frees up space on business endpoints.
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.