will analyze your hard drives and display the file sizes and folder sizes so that you can easily check the distribution of your disk space. This shouldn't even be necessary. It should be in Windows...
I use it often, no complaints so far, it calculates large folders easily. Very helpful when trying to build a disc image to fit a size constraint. (23.2GB) (4.6GB) etc...
If you're paranoid about it scanning all your files just block the program .exe in your advanced firewall (windows) so it can't possibly call home.