Tapulous made its iPhone music game Tap Tap Revenge free just before Christmas, with the aim of making money from ads and in-app song purchases. In the first 24 hours after going free, the game was downloaded 300,000 times. A week later, and it had racked up two million new downloads. On Christmas Day alone, 700,000 people downloaded it. Tapulous signed an exclusive deal with mobile advertising firm AdMob earlier last year.