Here’s an application I created for OS X which grabs new stories/articles that are posted to slashdot and reddit front pages (you can’t enter any site yet but it works with RSS). The app is meant to be run off focus (behind other windows) and it will keep a list of stories read in order to tell which stories are new. As you click on the new stories you want to read, they will disappear and once the window is put in the background, it will open the chosen articles in the default browser and remove the new stories from the list.
I created this app as it acts more like an RSS-diff program and simply tracks and monitors changes in RSS stories. The busier the feed the better as this program will basically keep a log of stories until you check them out. Let me know if you find this program useful and/or have any suggestions on how to make it better!