Publisher's description
a hard disk usage visualization tool. An extended pie chart displays all major files and folders. The directory levels are represented by concentric rings. Information on a particular item of the chart is available by moving the cursor over.
Seriously great.
Very simple, it shows your hard drive usage as a very good looking but clear Pie chart. Click on a slice(directory) and you can dig deeper into that directory and see what subdirectories/files are taking up how much space.
It doesn`t get any simpler or prettier than this =)