Gmail and K9 mail let me set different notification for each email account. Facebook, Facebook messenger, Android messages, Hangouts, Google+, Google calendar, UberSocial. They all let me change a custom notification sound other than the system default. Right now I set my system notification to a doorbell, then set all the apps out can to something else. That way if I get a doorbell sound, it's usually the Lockitron unless it's one of the few that don't let me change it.