In this chapter, we present Repovizz, an online platform for open-access and visualization of time-aligned multimodal data streams, where users can upload recorded data and navigate, playback, or edit existing datasets via a standard Internet browser. We expose the motivation behind its technical challenges and developments, the system internals, a use case example, and some thoughts about future challenges. In order to facilitate the sharing of multimodal recordings and extracted descriptors and annotations, Repovizz serves as a hosting platform and data archival protocol through which multimodal data (audio, video, motion capture, descriptor signals) can be stored, visualized, annotated, and selectively retrieved via a web interface and a dedicated API. The Quartet Dataset serves as a graphical example of how to use Repovizz, involving the recording, analysis, archiving, and cloud-based interchange of multimodal string quartet performance data as part of a collaborative research project on ensemble music making.