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>
If you like the plugin, consider supporting the author through http://www.brownlowdown.net/webdev/feedaggregator/#donate.

feedgator

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

Matthias Pfefferle

ActivityStreams (<a href="http://www.activitystrea.ms" rel="nofollow ugc">activitystrea.ms</a>) support for your WordPress-blog
ActivityStreams is an open format specification for activity stream protocols, which are used to syndicate activities taken in social web applications and services, similar to those in Facebook’s Newsfeed, FriendFeed, the Movable Type Action Streams plugin, etc.

ActivityStream extension

ActivityStrea.ms feeds for WordPress (Atom and JSON(-LD))

feedgator vs ActivityStream extension