IT 442: Windows Operating System

WinDirStat is a disk usage statistics viewer and cleanup tool for various versions of Microsoft Windows.
For Linux, you are looking for KDirStat (apt-get install kdirstat or apt-get install k4dirstat on Debian-derivatives) or QDirStat and for MacOS X it would be Disk Inventory X or GrandPerspective..
Its interface allows you to see exactly what’s using space on your hard drive at a glance.
you can download a portable version of WinDirStat from PortableApps.com if you’d like to take it with you and use it on various PCs without installing it first.
WinDirStat doesn’t offer a portable app on its website
WinDirStat is a free and open-source graphical disk usage analyzer for Microsoft Windows
WinDirStat
WinDirStat - Wikipedia

TreeSize Free is a good alternative to WinDirStat. It's simpler
The disk space manager TreeSize Free tells you where precious disk space has gone.
TreeSize is a disk space analyzer written by JAM Software.
TreeSize has native 32 and 64-bit support for all Windows versions and client/server versions currently supported by Microsoft
TreeSize
Microsoft-TreeSize
TreeSize - wiki

SpaceSniffer is a freeware computer disk space analyser from Uderzo Software for Microsoft Windows platforms
It uses a treemap to visualise disk usage.
SpaceSniffer doesn’t have the directory list included in WinDirStat
It’s just a graphical view that displays folders and the files in them by relative size
SpaceSniffer - wikipedia