BlogSieve

BlogSieve is a free tool that creates new feeds from existing feeds. Use BlogSieve to filter, merge, sort and strip any valid feeds into a new feed in any format you choose.

Website: http://www.blogsieve.com/

FEEDcombine

As the name suggests, it allows you to combine feeds in a seamless manner. You can set up as many combined feeds as you want, either using the predefined links or by entering your own favourites.

Website: http://www.feedcombine.co.uk/

Feed Informer

Feed Informer is a parser, regenerator, and syndicator for, and of, RSS and Atom feeds. It lets you do things like:

• put the content of RSS or Atom feeds on your own site(s)
• syndicate your blog’s content and/or links to other sites
• mix multiple feeds together into a single feed (Atom and RSS)
• convert RSS to Atom, and vice versa
• filter RSS and Atom feeds
• turn RSS and Atom feeds into a JavaScript include to use anywhere (even free Web space)
• turn feed(s) into WAP pages for cellphone use
• merge all blog mentions of your company onto a single page
• have your local weather update on your page(s) automatically
• merge RSS services with your Web site

Website: http://feed.informer.com/

feedkiller

feedkiller provides an rss mix service. with this tool you can put a variety of content into your website or favorite rss aggregator with a single rss feed. The setup is extremely simple and it is completely free.

Website: http://www.feedkiller.com/

FeedMingle

FeedMingle makes lives simpler for web designers/developers, feed readers, bloggers, or just anyone who wants to merge two or more RSS / Atom feeds into one. It mixes all the feeds provided and creates one RSS feed, Atom feed, JSON feed, and a html widget to simply paste into your website or blog.

Website: http://feedmingle.com/

RSS Mix

Mix any number of RSS feeds into one unique new feed.You can then point a parser at the new feed and display a mix of stories from various sources on your website.

Website: http://www.rssmix.com/

xFruits

xFruits is a free and multifunctional web service that enables you to do almost anything with RSS feeds. There are 11 different feed tools you can use. For example you can aggregate multiple RSS feeds into one, convert feeds into PDF, convert feeds to speech, create a mobile website from any feed, get feeds delivered to your email address and more.

Website: http://www.xfruits.com/

Yahoo Pipes

Yahoo Pipes is a powerful composition tool to aggregate, manipulate, and mashup content from around the web. Like Unix pipes, simple commands can be combined together to create output that meets your needs:

• combine many feeds into one, then sort, filter and translate it.
• geocode your favorite feeds and browse the items on an interactive map.
• power widgets/badges on your web site.
• grab the output of any Pipes as RSS, JSON, KML, and other formats.

Website: http://pipes.yahoo.com/pipes/

Easy RSS Mixer

If you want to combine several RSS feeds into one, Easy RSS Mixer is a great solution for you. No special knowledge in the field of RSS is required for working with Easy RSS Mixer. All you have to do is add source RSS feeds. The program will do all the rest!

Easy RSS Mixer supports not only all existing variations of the RSS format, but “understands” the RDF and Atom formats as well. The program can run in a completely automatic mode. Besides, Easy RSS Mixer has a built-in FTP client, a scheduler, a keyword filter, a previewer, a synonymizer and a built-in directory of popular RSS feeds.
Price: $31.95

Website:http://www.extralabs.net/easy-rss-mixer.htm

Feed Mix

Feed Mix is an RSS editor, which is powerful enough for RSS gurus yet refreshingly easy for RSS first timers. It lets you create, edit and publish the unlimited number of RSS feeds and podcasts. re-mix rss feeds, rss mesh, re-syndicate feeds. Unique to Feed Mix is its ability to create a new RSS feed or a podcast from several existing feeds. The program gives a great host of useful tools, including a WYSIWYG feed editor, a built-in RSS reader, a blog client, an HTML editor, an image editor, an XML editor and an FTP upload facility. All these and other tools are delivered in an intuitively transparent user interface that makes RSS creation and maintenance surprisingly simple even for a rookie.
Price: $34.97

Website: http://www.extralabs.net/feed-mix.htm

RSSmesh

The rssMesh.php script allows you to produce an RSS feed by taking the latest items from multiple feeds.
Price:$29.95

Website: http://www.feedforall.com/rssmesh.htm