I just started hacking on this a few weeks ago, so it's still premature and API is not stable. But apparently lots of people are getting excited about this software and of course, I'm not an exception.
With this you can get RSS feeds using various sources, like Bloglines, Google Reader, My Yahoo! and just a remote OPML, then (optionally) filters the feed content using social bookmarking services like del.icio.us, Digg.com and BlogMarks, then publish the updates in various ways: Gmail (recommended!), XHTML, PSP, iPod, RSS, Atom, metaWeblog etc.
Plagger is a platform to "do something with RSS/Atom feeds" and everything is implemented as a plugin, which can be enabled/disabled based on "rules". You can also create a smart feed with rules, like "entries tagged with Perl", or "entries bookmarked by more than 10 users on del.icio.us". Cool, huh?
Because it's a DIY kind of technology, it's tough for newbies, yet. But if you're interested in hacking on this, we have a website with lovely Trac installed and mailing list. We're in the IRC channel #plagger at freenode.net too.