WinDirStat

WinDirStat is a disk usage statistics viewer and cleanup tool for various versions of Microsoft Windows.

Note: if you are looking for an alternative 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.

Please visit the WinDirStat blog for more up-to-date information about the program.

On start up, it reads the whole directory tree once and then presents it in three useful views:

The directory list, which resembles the tree view of the Windows Explorer but is sorted by file/subtree size,

The treemap, which shows the whole contents of the directory tree straight away,

The extension list, which serves as a legend and shows statistics about the file types.

[출처 : https://windirstat.net/]