Process Monitor - Monitor file system, Registry, process, thread and DLL activity in real-time.
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
FSMonitor - FSMonitor is a macOS app that monitors all changes in the file system, including file creation...
TreeSize - TreeSize tells you where precious disk space has gone to.
DaemonFS - DaemonFS is a real time file monitoring software.
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.