Many of us here around the TUAW home office love Hazel ($21.95), the great folder-based automation utility that you can set up to run various rules to process (e.g. move, copy, sort) your files. However, we also like free, and so I was intrigued by a new application called File Action that is basically a kind of Hazel-light.
File Action concentrates on only one task -- moving files -- but like Hazel you can set it up to move those files on the basis of various rules. While less sophisticated than Hazel it can definitely handle useful tasks like sorting your downloads folder on the basis of file extensions, etc.
While I wouldn't give up the power of Hazel, if your file sorting needs are basic (and your wallet light), File Action is worth a look. It's a free download from Tom Hancocks.