Tok! is a collaborative acoustic instrument application for iOS devices aimed at real time percussive music making in a colocated setup. It utilizes the mobility of hand-held devices and transforms them into drumsticks to tap on flat surfaces and produce acoustic music. Tok! is also networked and consists of a shared interactive music score to which the players tap their phones, creating a percussion ensemble. Through their social interaction and real-time modifications to the music score, and through their creative selection of tapping surfaces, the players can collaborate and dynamically create interesting rhythmic music with a variety of timbres.