RSS mixers

• Yahoo! Pipes
  an advanced RSS mixer with a graphical user interface; supports simple operators, filters, and many advanced functions
   
• Advanced RSS Mixer
  combines different free RSS feeds (news, press releases and articles) into one, so you can use it on your website. Advanced RSS Mixer can automatically download new RSS feeds, merge them together and upload it to your server - all without your intervention.
   
• 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.
   
• Feed Informer
  a parser, regenerator, and syndicator for, and of, RSS and Atom feeds
   
• FeedJumbler
  a web-based application that allows you to convert a RSS or Atom-based feed into RSS, Atom and/or HTML and JavaScript, Merge several RSS or Atom-based feeds into one combined RSS and/or Atom feed, put an RSS feed (or merged feed) on your webpage using an IFrame or JavaScript)
   
• feedkiller
  provides an rss mix service. with our 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.
   
• FeedStitch
  Take your jumbled mess of feeds and make them one.
   
• KickRSS
  takes multiple RSS or ATOM feeds, combines them, and displays them as a single RSS feed or a webpage at an easy-to-remember URL.
   
• RSS Mix
  mix any number of RSS feeds into one unique new feed
   
• RSSmesh
  a PHP script used to merge multiple RSS feeds into a single RSS feed.
   
• ChimpFeedr
  Enter a bunch of RSS feeds into ChimpFeedr, and it will mash 'em up into one master RSS feed. You can also use that master feed for your RSS-to-email campaigns.