A while ago I wanted to make a service that could take an RSS feed, apply some filters and give me a new feed. It’s a good thing I didn’t because Yahoo has done it so much better than I ever could have done! Yahoo Pipes is a beautiful example of interactive HTML (very Web 2.0) and a fantastic service.
Specify your data sources (CSV files, feeds (it can even auto-discover feeds), pages, Flicker, etc), mix them, filter them, loop them, RegEx them, you name it, and output it all in a nice, neat feed.
Drag boxes on to the page, drag to connect them and fill in the blanks. It’s really easy to use!
A beautiful piece of software… There’s tons of other stuff you can do with it so check out their blog for hints and features.