An aggregatorcommonly known as a feed reader, RSS reader or news reader is a software program (such as iTunes) which is installed on your computer or a Web application (such as Bloglines) which aggregates or “pulls in” syndicated web content such as news headlines, blogs, and podcasts in a single location for easy viewing.
The syndicated content an aggregator will retrieve and interpret is usually supplied in the form of RSS or other XML-formatted data, such as RDF/XML or Atom.
News Sites as aggregators
Some websites such as Digg, Reddit, Stumbleupon and Yahoo Buzz which allow users to rate and submit articles function as a news aggregator site because they contain much user submitted data.
Social Media Aggregators
Some web applications such a friendfeed function as a social media aggregator. It allows you to access all of your aocial media sites from on e place.