du
Computer program
du is a standard Unix program used to estimate file space usage—space used under a particular directory or files on a file system. A Windows commandline version of this program is part of Sysinternals suite by Mark Russinovich. Wikipedia
Developer(s): Various open-source and commercial developers
Initial release: 3 November 1971; 52 years ago
Original author(s): Dennis Ritchie; (AT&T Bell Laboratories)