Which is why many of us value Hazel so highly. It's a utility that monitors folders on your Mac for events that you define--a file being added or modified, for example. When particular events take place, automatically initiates actions that you've defined, such as moving the file to another folder, renaming it, or changing its label. I praised as one of the handiest apps on my hard drive, and Hazel 3 makes it even handier.
As in previous editions, Hazel 3 is a System Preferences pane. Open it up and you see straightforward interface: On the left there's a list of folders that the utility is monitoring, on the right is a list of the rules that you've defined for the selected folder. To start monitoring a folder, you click the plus-sign (+) button and choose the folder.
Creating rules is similarly straightforward, and if you've ever created a rule in Mail, the process will feel familiar. Each rule has two components, conditions and actions. For conditions, you choose from a pop-up list of attributes: Name, Kind, Date Added, and many more. If you select Other from that menu, you can choose from almost any file- or folder-attribute that OS X tracks. Next to that is a pop-up list of operators (is, contains, is less than, and the like); the list changes depending on the attribute. Finally you have a test field, where you define the value(s) for matching the attribute and operator (Date Added is Today, for example).
Once you've defined your conditions, you specify the actions Hazel will perform when those conditions are met. Actions can vary from the basic (Move, Rename, Set Color Label) to the not-so-basic (Run AppleScript, Run Automator Workflow, Run Shell Script). And not only can you use Hazel to keep an eye on folders you already use, you can also use it to create special folders that do useful things when you drag files into them.
Hazel 3 doesn't really change any of these basics, but it does tweak them and make them more powerful. One of the most-welcome improvements is the capability to nest conditions. If you've created a smart folder in the Finder or a smart playlist in iTunes lately, you know how handy nested conditions can be--by combining multiple, hierarchical And, Or, and Not statements, you can make Hazel match files with incredible precision and flexibility. (For example, Name contains "Hazel" or "review," added to the folder today or last week but not last Friday or Tuesday, and item's contents contain the word "incredible.") You can also specify custom conditions via AppleScript or shell scripts--the script just has to return the value True--which enables you to test against even more file and folder attributes and apply even fancier conditional logic.