Hazel is a flexible utility designed to help you tidy up files and folders--especially in your Downloads, Desktop, and Trash--and keep them organized with rules that you specify. You access Hazel through a System Preferences pane, where you can create Mail-style rules to execute a wide variety of actions. For example, Hazel's built-in sample rules include options for cleaning up your Downloads folder, such as automatically moving images and music into your Pictures and Music folders respectively. These sample rules only hint at Hazel's capabilities, though, and you can set the app to automatically import into iTunes and iPhoto, add comments, copy, rename, and sort files, and more. You can even have Hazel run an AppleScript or Automator based on any criteria that you set--and Hazel can use any Spotlight attribute in its rules (so, for example, you could even apply rules to images based on shutter speed).
Hazel can also keep an eye on your Trash, by deleting files after a certain amount of time or by never letting the Trash get over a certain size. A new App Sweep feature lets Hazel double as an uninstaller: whenever you drag an app to the Trash, Hazel will move its support files along with it. Once you set up your rules, Hazel runs quietly in the background--or you can have it notify you of certain actions using Growl. More casual users won't want to spend money on a file cleanup utility, but Hazel is an excellent time-saving app if you're willing to invest some effort in setting up personalized rules for your particular workflow.