Would you happen to mean readers with filtering tools? If so I'm interested as well.

I know Thunderbird technically has them, but I've had trouble making them work as effectively as I'd like. RSSOwl had some that were easier to work with, but stopped being updated. There's now a fork of it called RSSOwlnix, but I haven't taken the time to see whether it still works as well or not. May be worth looking into though...