Disk Sorter Free is a powerful tool for investigating a hard drive and better understanding the range of files it contains.
To use the program you must first choose an "Input Directory", a root folder where Disk Sorter should begin its scan ("C:\" if you want to check all of drive C:, say - you can add more than one folder, if you like). Click "Classify", make sure "Default File Classification Plugin" is selected, and click "Classify". Disk Sorter will then check and group every file in the folder trees you've specified (up to a maximum of 500,000 and 2TB storage capacity in the free version).
Once the scanning is over (and it only takes a moment) Disk Sorter displays a list of Categories - "Movies...", "Music...", "Images..." and so on - with the hard drive space taken by each. You'll see at a glance which category is taking up the most drive space, and double-clicking that category will drill down to help you find out more.
That's just the start, though. Once you've double-clicked a category like "Movies, Clips and Video Files", say, you can organise and group those files in many different ways. Select "By Extension", say, and you'll be able to view the results by video type. Choosing "By File Size" provides an easy way to identify the very largest clips. And you can even classify files by creation, modification or last access date, useful if (for instance) you need to pick out files which have been created recently.
Better still, if you identify a group of files which you don't need, Disk Sorter can help you do something about that. Right-click a selected group of files and you'll find options to delete or compress them, copy or move them somewhere, and more.
There are some annoyances here. In particular, the filtering system is somewhat less than intuitive, and you should expect to spend some time exploring until you figure out what's going on. But, if you need a powerful and versatile tool for classifying, categorising and reporting on your files, then Disk Sorter is one of the best free options around.
Version 6.20: "adds the ability to save graphical summary PDF reports including various types of file classification pie charts, history line charts and statistics showing the number of files and disk space usage per file type, extension, user name and how the number of files and disk space usage are changing over time."