want web-based aggregator that outputs RSS

["tjmccormick2000" <yahoo-groups-syndication@tjm.org>]

ok, I've been looking at various aggregation tools for a while, but 
can't quite tell if one exists with which I could achieve my dream 
specs, as described below. Can anyone advise me on what, if any, 
tool/service/configuration could currently implement the following 
requirements, or come closest?

1) web-based service, to which I could go and create one or more 
lists of RSS feeds to be aggregated, including arbitrary (i.e. user-
submitted) RSS URLs that I supply. 
2) for each RSS feed list, the service would (like Meerkat) 
periodically check the feed for new stories, and add any new items to 
a single, reverse-chronological article list, while maintaining a 
label to identify the item's source.  
3) this resultant article feed is, itself, available as a web-
accessible RSS feed. 

The service would be web-based (i.e., server-side) so that it could 
operate constantly, even if my own computer is off or offline. 
  Can this be done? Would someone offer this service for a fee? 

thanks,
Tim

------
Tim McCormick
http://www.tjm.org  /  www.opencritic.org  /  www.opencontentlist.com