*Denotes joint first authors. Group synchrony — the temporal coordination of rhythmic behaviors between multiple individuals — is fundamental to human social interaction. Although synchrony often occurs in large groups such as orchestras or sports teams, most scientific knowledge comes from investigating dyads, typically in joint music-making contexts. Scaling investigation beyond the dyad presents significant methodological challenges, including building measurement platforms that simultaneously acquire data from many individuals and developing paradigms that can be systematically scaled across n-person groups. Here we present "The Tapping Orchestra", a low-latency platform for measuring group synchrony at brain (EEG) and behavioral levels during musical interaction. Accessible to both musicians and non-musicians, participants tap sensors to produce successive tones in a melody, enabling the experience of music production without learning complex auditory sequences. We describe the platform's design, implementation, and validation of measurement accuracy for hardware and software. We report findings from a proof-of-concept study adapting an established dyadic synchronization paradigm to larger groups, demonstrating the platform's scalability for measuring synchrony across diverse group sizes. Together, technical and empirical validation of The Tapping Orchestra establishes a methodological foundation for investigating how coordination dynamics scale to larger group behavior, paving the way for systematic approaches to multi-person neuroscience.