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

I looked this up when I had to figure out what was using up all my space in my C drive (partitioned to 50GB), but was sick of right-clicking each folder to view its size. Great little program for when Disk Cleanup doesn't free enough space.