tranglos
However, what I really need is to redirect all file requests from /free/files/a.zip to /files/a.zip - and this does not work with the redirect above. Do I have to create an item for each individual file?
(Also, placing the "ErrorDocument 404" directive in .htaccess does nothing (still getting the same 404 pages from Joomla), but that has probably nothing to do with your extension.)
In the current release "FromURL" can be dinamic using regular expressions, but "ToURL" is always static, so you are right. In the next release I'm planning to introduce a macro (like {siteurl}) or something like this that enable to redirect to a dinamic destination. I hope in future I can deserve the missing star. Enjoy.

