First of all, people who called Google+ a “killer app” the week it was launched are either Brinlickers, or just completely misusing the word.
Second, rapmushi is truly a killer app for the iPhone.
I fucking detest Apple and have refused to buy anything they made since Steve Jobs sent me an email demanding money for a previously free macdotcom email address ~12 years ago and declared that “the era of free is over.”* However, if I could overlook the kind of mindlessness and snobbery that that Apple culture perpetuates, I might buy an iPad just to play this app; it’s that good. The last time I was moved to purchase a new system by a software title was by Parappa the Rapper on the original PlayStation.
*Actually, this statement was and still is true for Apple users, but he was talking about free services like webmail. The really ironic thing is that this truly outstanding rap mushi app is free.