ZetaWatch - Manage ZFS volumes in the menu bar
SpaceMonger - SpaceMonger helps you understand what's occupying your hard drive and more effectively clean it up without worrying about losing anything important in the process.
Baobab - Distributor of workload automation, financial statement reporting, data access, IT Asset Management and Service Desk software solutions.
Filelight - Filelight is an application to visualize the disk usage on your computer.
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
htop - htop - an interactive process viewer for Unix. This is htop, an interactive process viewer for Unix systems. It is a text-mode application (for console or X terminals) and requires ncurses. Latest release: htop 2.