clipped from: www.blogsieve.com   
BlogSieve is a free web-based tool that creates new feeds by filtering, merging and sorting existing feeds. The BlogSieve engine accepts virtually every (valid) feed format, processed results are then exported into any feed format you choose.

Have you ever been frustrated by the limitations of Atom, RDF and RSS feeds? Is it difficult for you to find the "perfect" feed because most feeds only touch on your desired focus? If so, then it's time you looked at 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.

The BlogSieve engine offers the following filter, merge, sort and strip functions:

Best of all, you can combine multiple filter, merge, sort and strip functions into a single new BlogSieve based feed.