Children's fantasy about rival cat tribes in future

Some time between 2005 and 2015 I saw a new children's book in the library, didn't check it out or read it at any length, and don't remember the author or title. It was set in a possible future and was about rival cat tribes. I remember "Ferals" and "Indoors" as names and can't tell whether "Ferals and Familiars" is a book or relates to the same series.

This search was suggested by the Library Thing Hunt clue, but no worries, I'm out of that. Life's too short and I spend too much of it clicking on links and waiting for pages to open, at best.

>1 PriscillaKing: That sounds like Warrior Cats by Erin Hunter