From Maurice Michalski:
Guido shows a graphical representation - similar to a pie chart - of the used space of directory or an entire disk. You can navigate within the pie chart to let it show parent or child directories. Chart data can be exported as hierarchical XML file, as a file list (plain text file) or you can save the pie chart as a picture file (PNG and JPEG). You can also use drag&drop to analyze certain directories.