Social connection is a fundamental determinant of wellbeing, yet the emerging landscape of consumer neurotechnology is oriented almost entirely toward individual experience. This paper presents Collective Calm, a portable multi-subject brain-computer interface (mBCI) that asks whether shared EEG-driven neurofeedback can support a felt sense of collective calm and prosocial connection in small groups. Using consumer-grade EEG headsets, the system translates participants’ real-time brainwave signals into a shared generative art environment that responds to, and reflects, the group's collective physiological state. An autobiographical research-through-design probe with two participants demonstrated consistent experiential evidence of shared focus and collective awareness during neurofeedback exposure, while surfacing technical challenges that have since informed system refinement. The system has received ethics approval for a human subjects study currently underway. At IH 2026, conference attendees will be invited to experience the installation directly, wearing EEG headsets and co-creating a live neurofeedback artwork with their collective brain signals. This work contributes a novel interaction paradigm, a proof-of-concept probe, and an open research agenda at the intersection of consumer neurotechnology and collective health.