Feed(Aggre)gator takes a list of RSS feeds and creates a single list of RSS items from those feeds to be displayed as a widget. You can select how many items you want to display and whether you want to show the entries chronologically or you want to show the latest entries from each feed listed.
You can also opt to display the date associated with the RSS item as well as the author of the item.
<h3>Donate</h3>
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feedgator

Feed(Aggre)gator merges a group of RSS feeds into a single widgetized list.

padraic

Implements <a href="http://pubsubhubbub.googlecode.com/svn/trunk/pubsubhubbub-core-0.1.html" title="the PubSubHubbub protocol" rel="nofollow ugc">the Pubsubhubbub protocol</a> based on the current PubSubHubbub Core 0.1 Specification and any changes since its publication. <a href="http://code.google.com/p/pubsubhubbub/" title="PubSubHubbub" rel="nofollow ugc">PubSubHubbub</a> is an open, simple web-scale pubsub (publish/subscribe) protocol capable of notifying one or more Hub Servers (e.g. the reference open source <a href="http://pubsubhubbub.appspot.com/" title="implementation on Google App Engine" rel="nofollow ugc">implementation on Google App Engine</a>) of your blog updates so they may be forwarded to any of your feed’s Pubsubhubbub enabled Subscribers as quickly as possible.
Any Pubsubhubbub enabled Subscriber can then receive an almost immediate update from any of your Hubs containing the actual update for immediate use. Subscribers know what Hubs to use when subscribing to your RSS 0.92, RDF/RSS 1.0, RSS 2.0, or Atom 1.0 feeds since this plugin will insert one or more links to your configured Hubs into these feeds.
WP Pubsubhubbub has the following features:
<ul>
<li>Supports multiple Hubs configured from the settings page</li>
<li>Pings all Hubs whenever you publish/edit a blog post</li>
<li>Adds suitable Atom namespaced link elements for each configured Hub to the top of your RSS 0.92, RDF/RSS 1.0, RSS 2.0, or Atom 1.0 feeds</li>
<li>Maintains compliance with the Pubsubhubbub 0.1 Core Specification and any outstanding amendments</li>
<li>WP Pubsubhubbub utilises a Pubsubhubbub Publisher implementation which is fully unit tested for reliability and specification conformance, based on Zend Framework’s upcoming Pubsubhubbub component for which I am the lead developer.</li>
<li>Where no replacement Hubs are configured, WP Pubsubhubbub defaults to the reference Hub hosted on Google App Engine. This is a very reliable Hub. We also default to using the Superfeedr Hub as an alternative to ensure reliable service. You may replace or add to this list as needed.</li>
<li>Version 1.1.0 also enables Hub notification of changes to your RSS 2.0 Comment Feeds</li>
</ul>
As the specification authors state on the main Pubsubhubbub site, the protocol is decentralized and free. No company is at the center controlling it. Anybody can run a hub, or anybody can ping (publish) or subscribe using open hubs.

WP Pubsubhubbub

Implements a Pubsubhubbub Real Time Publisher informing Planet Earth of your updates now, not later!

feedgator vs WP Pubsubhubbub