lightsystem

The plugin is configurable letting you define what feeds to read and how often to read them. It also lets you decide whether you want to store the external images locally, inserting them into the media gallery, or otherwise simply hotlink them (that is the default).
You will find these settings in your administration page on the Settings->RSS Settings sub-menu.
Check out the <a href="https://github.com/LightSystem/WordPress-Plugin-RSS-Sync" rel="nofollow ugc">project on GitHub</a>.

RSS Synchronisation

Use this plugin if you wish to read external RSS feeds into WordPress posts.

Matthias Pfefferle

IndieWeb

joshfraz

This plugin is a simple way to let people know in real-time when your blog is updated. PubSubHubbub/WebSub is widely adopted and is used by Google Alerts and many other services. Subscription requests are relayed through hubs, which validate and verify the request. Hubs then distribute new and updated content to subscribers when it becomes available.
This plugin:
<ul>
<li>Sends realtime notifications when you update your blog</li>
<li>Supports multi-user installations (WordPress MU)</li>
<li>Supports multiple hubs</li>
<li>Supports all of the feed formats used by WordPress, not just ATOM and RSS2</li>
<li>Supports latest specs
<ul>
<li>PubSubHubbub <a href="https://pubsubhubbub.github.io/PubSubHubbub/pubsubhubbub-core-0.4.html" rel="nofollow ugc">Version 0.4</a></li>
<li>WebSub <a href="https://www.w3.org/TR/websub/" rel="nofollow ugc">W3C Version</a></li>
</ul>
</li>
<li>Announces which hubs you are using by adding <code><link rel="hub" ...></code> declarations to your template header and Atom feed</li>
</ul>
By default this plugin will ping the following hubs:
<ul>
<li><a href="https://pubsubhubbub.appspot.com" title="Demo hub on Google App Engine" rel="nofollow ugc">Demo hub on Google App Engine</a></li>
<li><a href="https://pubsubhubbub.superfeedr.com" title="SuperFeedr" rel="nofollow ugc">SuperFeedr</a></li>
<li><a href="https://websubhub.com" title="WebSubHub" rel="nofollow ugc">WebSubHub</a></li>
</ul>
Please contact me if you operate a hub that you would like to be included as a default option.

WebSub (FKA. PubSubHubbub)

Best Update Plugin

A better way to tell the world when your blog is updated.

RSS Synchronisation vs WebSub (FKA. PubSubHubbub)