Plagger is a RSS/Atom feed aggregator which is written in Perl. It’s a plug-in that can be completely reused and mashed-up to create new apps for feeds.
In other words, it’s an open source feed routing system which you could also call a mash-up creator. It can enhance your feeds, combining and aggregating content into one single feed. There’s also email notification. You can track your feeds through your email. Once received, you can organize and archive feeds in your inbox without using a separate app. On the Plagger homepage you’ll find guides and documentation along with a wiki and roadmap. There’s also a Plagger repository and list of hacks.
Plagger.org In Their Own Words
“Plagger is a pluggable RSS/Atom feed aggregator written in Perl. Everything is implemented as a small plugin and you can mash them up together to build a new application to handle RSS/Atom feeds. Ray Ozzie said RSS can be Unix Pipe of the Internet and that way Plagger is an Unix shell for Web 2.0!
If you’re familiar to Perl, Plagger is like a blosxom or qpsmtpd of RSS/Atom remixer.”
Why Plagger.org It Might Be A Killer
Plagger opens up RSS; it’s flexible. Plagger is a useful for detecting site updates with or without fees. You can store feeds to your mobile devices e.g. iPod, or post updates to Twitter using your account.
Some Questions About Plagger.org
What about the competition? How is Plagger going to get their own loyal users? 
