dupeGuru - dupeGuru is a tool for finding duplicate files on your computer.
ncdu - A disk usage analyzer with an ncurses interface, aimed to be run on a remote server where you...
AllDup - AllDup is a freeware tool for searching and removing file duplicates on your Windows computer.
Baobab Disk Usage Analyzer - Baobab Disk Usage Analyzer is one of the light-weight disk analyzers that offers you a chance to view and monitor the disk usage & folder structure without any hassle.
Czkawka - Multi functional app to find duplicates, empty folders, similar images etc.
K4DirStat - K4DirStat is the successor of former KDirStat.