Easy to Use
As simple as:
require('rss_fetch.inc');
$rss = fetch_rss($url);

Parses RSS 0.9 - RSS 1.0
Parses most RSS formats, including support for 1.0 modules and limited namespace support. RSS is packed into convenient data structures; easy to use in PHP, and appropriate for passing to a templating system, like Smarty.
Integrated Object Cache
Caching the parsed RSS means that the 2nd request is fast, and that including the rss_fetch call in your PHP page won't destroy your performance, and force you to reply on an external cron job. And it happens transparently.
HTTP Conditional GETs
Save bandwidth and speed up download times with intelligent use of Last-Modified and ETag.
See HTTP Conditional Get for RSS Hackers
Configurable
Makes extensive use of constants to allow overriding default behaviour, and installation on shared hosts.
Modular
rss_fetch.inc - wraps a simple interface (fetch_rss()) around the library.
rss_parse.inc - provides the RSS parser, and the RSS object
rss_cache.inc - a simple (no GC) object cache, optimized for RSS objects
rss_utils.inc - utility functions for working with RSS. currently provides parse_w3cdtf(), for parsing W3CDTF into epoch seconds.