Onyx by Titanium - This website provides operating system utilities for macOS

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

AVG PC TuneUp - Peak performance for your PC. Keeps it going for longer. - More Speed Turbo Mode

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.

Clean Master - Some users swear by it, some call it a glorified snake oil that does more harm than good. That can be said about any snake oil, but what specific brand of snake oil can boast almost a billion downloads around the world?

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.