This one's almost a cop-out, since all Windows users should know about WinDirStat by now. This app has been out for nearly 15 years, and it's one of the most helpful tools you can use to clean up your hard drive.
WinDirStat is completely free; it shouldn't be, given how great it is, but it is. To make it work its magic, you just download a single file — that's it. Though we wish there was a portable version of WinDirStat, the installation process doesn't take very long (and barely any space). When you close out of the installation routine, WinDirStat loads by default.
When the app opens, you select a location you want WinDirStat to scan. This could be your entire primary hard drive, a secondary hard drive you use that has been mysteriously filling up with storage, or just the contents of your Windows user folder (or Pictures, or Downloads, etc.) The program then begins to work its magic, rooting through every folder, subfolder, and file within the area you selected.
Good god, Square Enix.
WinDirStat displays the contents of what it finds as a large, unruly graphic at the bottom of the app. It also shows your folders in ascending order by size and continues to do so as you click through them to go deeper and deeper into your drive's contents. This makes it incredibly easy to find mysterious folders that are eating up gigabytes of space (or worse), which might very well be the result of an accidental copy-and-paste of a large movie, some crazy thing going on with your Temporary files in Windows, or a huge stash of
porn Linux distributions you forgot about.
Whatever your file poison, WinDirStat is the antidote for a hard drive that's running out of space — which I'd wager is user error seven times out of ten, and Windows' fault the other three. While you can use WinDirStat to even create special routines for cleaning your drives and folders, like deleting every .BAK or .TMP file it can find, you're better off using WinDirStat's helpful information as the guiding light for a big deletion spree through File Explorer. Reclaim your precious space, Windows users. It doesn't get easier than this.