Prevent Restore is an easy-to-use tool for wiping the free space on your hard drive, ensuring that no confidential files can be recovered.
The program has plenty of configuration options. You can have it tell Windows to clear your paging file at shutdown, for instance. You can opt to have it empty your Recycle Bin first, which means those files will also be unrecoverable. And Prevent Restore supports five methods of overwriting free drive space, from simply using spaces, random characters or digits, to standard algorithms like Gutmann and DoDD 5220.22.
Of course if you're working on a slow drive, with a lot of free space, which you're overwriting many times, then the cleaning process may take a while. But you can just leave Prevent Restore running while you go and do other things, and it's able to optionally close your PC down when it's finished.
What you don't get here is any option to securely delete specific files or folders; it's the entire drive, or nothing at all.
In some ways this is a good thing (Prevent Restore can't be used to accidentally delete anything as it only overwrites free space).
But in other ways it's a very bad approach, because overwriting all your free drive space doesn't only wipe confidential documents. It will also erase regular files which you may find you want to undelete at some later date.