WinDirStat is a disk usage statistics viewer and cleanup tool for Windows based systems.

Baobab is a disk usage analyzer is a graphical disk usage analyzer for GNOME.

GrandPerspective is open source software for Mac OS X used for disk space analysis.

SpaceMonger is a tool for keeping track of the free space on your computer.

GdMap is a tool which allows visualizing disk space.

FolderSizes is a disk space management tool.

SpaceSniffer is a freeWare and portable tool application that lets you understand how folders and files are structured on disks.

DaisyDisk is a disk space analyzer for OS X.

Scanner is a tool uses a sunburst chart to display the usage of your hard disk or other media.

SequoiaView is a disk browsing tool based on the principle of treemaps.

RAWGraphs allows you to export visualizations as vector (SVG) or raster (PNG) images and embed them into your web page.