QDirStat

QDirStat shows disk contents as a folder tree sorted by size next to a coloured treemap in which every file is a rectangle of proportional size, so huge files and folders stand out at once. It includes statistics by file type, a size and age histogram, a view of system packages and configurable cleanup actions such as moving to trash or deleting. You can save a scan to a file and analyse a remote server. It suits a Linux workstation or server that has filled up. Limitation: there is no Windows version (use WinDirStat there), and on macOS only through third-party builds.