I’ve just released a project I’ve been working on, called FeedBlendr. Basically it allows you to create custom feeds by combining any number of existing RSS or Atom files into a single one. It’s got some funky AJAX-checking on URLs, and soon it will have some slick integration with FeedBurner which should allow me to do some very cool things with it.

Check it out and see if it’s useful – hopefully when combined with some other things I’m working on it’ll allow you to mash feeds up just the way you want them.