Keypirinha - A lightning fast and flexible keystroke launcher for Windows. No installation required (portable).
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
Listary - Listary is a revolutionary search utility for Windows
TreeSize - TreeSize tells you where precious disk space has gone to.
Alfred - Alfred is an award-winning app for macOS which boosts your efficiency with hotkeys, keywords, text expansion and more. Search your Mac and the web, and be more productive with custom actions to control 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.