Disk Usage Analyser(DUA) is a GNome ustility available for Linux. As the name indicates DUA scans the filesystem and finds out how much space is occupied by each directory and file. It then shows the usage along side a folder tree as a bar graph.When you click on a directory name, memory usage by each subfolder and files can be seen as an arc diagram on the right pane.
The Disk Usage Analyzer can be used to find out which directory or file uses how much space. It can be very helpful if you are trying to clean-up some Hard Disk Space from your PC. A similar tool for Windows is WinDIrStat at Sourceforge.net. but this one is a little less visaully attractive one. For KDE users KDirStat might be a solution.