RSS Aggregator is a set of PHP scripts that fetches, parses, and reconstitutes a set of RSS feeds into a single feed, maintaining the correct date order of the posts.
You will need PHP5 at a minimum. I'm not sure if there are any particular versions, but at present I'm developing under PHP 5.3.1 on Windows and PHP 5.2.6-3ubuntu4.5.
You will also require one of the SQLite extensions either compiled in, enabled in your php.ini, or available to dl().
I'm using a tool which takes RSS input, but has a woeful interface to add/remove feeds, and would prefer to simply edit a config file in Vim than use their clunky web interface.
Also, it gave me another reason to write a little compatibility layer for SQLite so that either SQLite3 or SQLite2 could be used almost transparently.
Because I'm strange like that.