This is a feature of the Finder that very few people use, yet it is so powerful. Folder actions allow you to perform an action to any file that is dropped into the folder. What you can do is only limited by what you can script, or what scripts you can find.
Start by creating a new folder and checking that folder actions are enabled by right-clicking (control-clicking) and selecting “Folder Actions Setup”.
Next, choose a script from the list to attach, or press the plus (+) button to navigate to one of your own scripts. Also, make sure the “Enable Folder Actions” checkbox is checked.
Most of the example scripts involve image manipulation and converting from one file format to another. Selecting one of these format converting scripts will mean, for example, that all jpeg images dropped into the folder will be turned into tiff images.
However, as I mentioned at the start of this tip, this is only a taste of what you can do. Any applescript, automator workflow or shell script can be attached, and therefore the possibilities are endless!