WinDirStat

Utility for Windows computers that shows usage statistics and can perform different tasks to clean the hard drive. View detailed information about hard drives and folders in a simplified tree view. Can display files grouped by extension and user view the space on hard drive for each category of files (videos, images, documents etc.).
 
It helps to manage hard disk space by viewing useful statistics displayed in an improved visual manner. Useful to analyze computers prior to clean process.