rsswatch lets you set up rules to match against RSS feeds and downloads files linked in matching entries. It was created to be used together with rtorrent's watch directory functionality, but you can probably find other uses for it as well.
rsswatch is actually comprised of two parts: a configuration UI which lets you add and remove rules using a web browser, and the actual rsswatch.php script which is meant to be run at a regular interval, preferably using cron.
You need to download the latest rsswatch release. Your web server has to have write permissions to rsswatch.conf for the web UI to work, and whatever user you use for the cronjob has to have write permissions to the target directory for your downloads.
NOTE! Don't piss off the websites you get the RSS feeds from - set cron to run rsswatch.php every 10 minutes, not more.
rsswatch is in the public domain. Do with it as you please, but don't expect me to support it. rsswatch was written by Martin Melin.