What is "windirstat"

WinDirStat is a free and open-source graphical disk usage analyzer for Microsoft Windows. It is notable for presenting a sub-tree view with disk use percentage alongside a usage-sorted list of file extensions that is interactively integrated with a colorful graphical display (a treemap). Created as an open source project released under the GNU GPL, it was developed using Visual C++/ MFC 7.0 and distributed using Sourceforge. The project was inspired by KDirStat, a KDE application for Unix-like operating systems.