This paper provides an overview of the design, prototyping, deployment and evaluation of a multi-agent interactive sound instrument named MOM (Mobile Object for Music). MOM combines a real-time signal processing engine implemented with Pure Data on an embedded Linux platform, with gestural interaction implemented via a variety of analog and digital sensors. Power, sound-input and sound-diffusion subsystems make the instrument autonomous and mobile. This instrument was designed in coordination with the development of an evening-length dance/music performance in which the performing musician is engaged in choreographed movements with the mobile instruments. The design methodology relied on a participatory process that engaged an interdisciplinary team made up of technologists, musicians, composers, choreographers, and dancers. The prototyping process relied on a mix of in-house and out-sourced digital fabrication processes intended to make the open source hardware and software design of the system accessible and affordable for other creators.