QuizUp is among the fastest-growing apps on the iPhone, and it barely spent a penny on marketing. That’s rare for a game industry that invests to boost app rankings and push installs. But QuizUp has become more than a game. It’s a trivia-driven social network, one in which niche audiences challenge each other on all manner of topics. Communities are forming around hundreds of categories, and they communicate by messenger and message boards. CEO Thor Fridriksson says the trivia is addictive and the social component is cohesive—which means brands want in. And his ultimate aspiration? “I’ve heard people say, ‘QuizUp me.’ The dream of any brand is to be turned into a verb,” he says. Adweek gave Fridriksson the QuizUp treatment.