This is bseifert's great WinDirStat utility which allows you to display the content of a directory in a very intuitive way as far as the size of each file and subfolder is concerned. With one addition: you can also specify which user(s) you are actually interested in. This is especially useful for sysadmins and users who exceed their quota on a network share, since they are not interested in all the files but only some/their own files.
It's the same as the original WinDirStat, so please refer to the original documentation. The user selection dialog (Active Directory object picker) is displayed immediately after the directory dialog. If you don't want to filter files for any user(s) then simply cancel the second dialog. Otherwise insert the user names and press OK.