PuTTY - Popular free terminal application. Mostly used as an SSH client.
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
MobaXterm - Enhanced terminal for Windows with X11 server, tabbed SSH client, network tools and much more
TreeSize - TreeSize tells you where precious disk space has gone to.
iTerm2 - A terminal emulator for macOS that does amazing things.
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.