BottomFeeder
A Smalltalk, desktop RSS Reader. Open source, runs on Windows, Mac, and various Unix flavors.
http://www.cincomsmalltalk.com/BottomFeeder/

TALAggregator
Multi-user web based RSS Aggregator. Caches feeds to MySQL database, handles bad RSS, and includes template driven interface.
http://www.owlfish.com/software/TALAggregator/

TheYoke
A simple RSS aggregator designed for use on the UNIX command line.
http://www.mackers.com/projects/theyoke/

Parss Project
The general idea behind Parss is to solve the problem of countless individual (desktop) RSS viewers randomly and redundantly transferring and processing almost exactly the same set of RSS feeds.
http://weblogs.at/parss/

Rnews
Server-side RSS aggregator written in php using MySQL as the back-end and uses magpierss for the RSS parser.
http://rnews.sourceforge.net/

Raggle
Open-source console-based RSS aggregator, written in Ruby, for Linux, Unix and Windows. Information for users and developers.
http://www.raggle.org/

phpNewsfork
Browser-based news channel and Weblog interface based on PHP, XML-RPC, and RSS. It uses the XML-RPC APIs from meerkat.oreillynet.com and syndic8.com, and does not require a database.
http://www.borho.net/news/about.html

Mercury News Readers
Displays RSS, RDF and Atom feeds. Available as screensaver, news ticker, Internet Explorer toolbar, and feed reader application.
http://oracle.2question.com/rss/

Sage
RSS and Atom feed aggregator extension for Mozilla and FireFox browsers.
http://sage.mozdev.org/

Wizz RSS News Reader
A simple RSS news reader extension for Firefox. Reads all versions of RSS. i.e. 0.90, 0.91, 0.92, 0.93, 1.0 (RDF) and 2.0.
http://www.wizzcomputers.com/WizzRss.php

MyHeadlines
Content syndication search engine and news reader that can be integrated into a website running PHP and MySQL.
http://www.jmagar.com/myh4/

Planet
Server software that combines several feeds together and publishes them together on one web page.
http://www.planetplanet.org/

Feed on Feeds
A Free PHP/MySQL based server-side RSS and Atom aggregator. All feeds are in one place, and users can read the latest news wherever they are.
http://feedonfeeds.com/

Pluck
A tool that automatically retrieves RSS feeds then delivers the results for scanning and customized sorting.
http://www.pluck.com/

RssDisplay
A quick Perl CGI to render an RSS feed in HTML for use in SSI on sites. This script does that very simply, yet with a small set of configurable options.
http://www.decafbad.com/twiki/bin/view/Main/RssDisplay

Rawdog
An aggregator written in Python that supports RSS 0.9, 1.0, 2.0, CDF and Atom feeds.
http://offog.org/code/rawdog.html

NewsFeed
A desktop RSS reader and aggregator in Python/Tk.
http://home.arcor.de/mdoege/newsfeed/

Rocketinfo Desktop
Search software for finding and sharing news with integrated solid RSS newsreader.
http://www.rocketinfo.com/

RSS-Planet
A program that displays RSS items based upon their geographical location on a map of the world. Requires xplanet or OSXplanet.
http://home.arcor.de/mdoege/rss-planet/

QuikView Channel Viewer and Bookmark Server
Full channel RSS / XML viewer and bookmark server. A portable, cross-platform, sidebar application. Able to read all RSS versions.
http://quikonnex.com/start/

CafeRSS
Information and download for an RSS aggregator using PHP.
http://barkerjr.net/webdesign/CafeRSS/

myRadio
Extension to Radio Userland aggregation from RSS to any data source, including XML, HTML, and SOAP.
http://brainoff.com/weblog/outlines/myRadio/

Yoono
A RSS reader/builder integrated into a social bookmarking application based on browser bookmarks. Includes a search engine, web monitoring and sharing functions.
http://www.yoono.com/

Feedjack
Feed aggregator written in Python and Django. Supports archives, tag clouds, multiple sites and themes.
http://www.feedjack.org/

The infoRSS Project
A lightweight RSS, ATOM, NNTP and HTML headlines reader for Firefox, Mozilla, SeaMonkey, Netscape and Thunderbird. Download, FAQ, screen shots, and Flash movie demos.
http://inforss.mozdev.org/

FIRST SAY
Open source RSS news aggregator designed to build collections of feeds and provide a first page presentation of feeds from many sources.
http://vbxml.net/