Multimedia environments provide multiple resources for expression, collaboration, and knowledge-creation. Yet there is much to be learned about the design of such environments, the forms of collegial discourse that take place, and the benefits of participation. To this end, we study the 2017 STEM for All Video Showcase, a multimodal environment, that enabled educational researchers to share and discuss short videos depicting their federally-funded work to improve STEM education. The event (http://stemforall2017.videohall.com), featured 171 video narratives, each accompanied by meta-data, an abstract, and its own discussion. This Showcase, funded by the National Science Foundation (NSF #1642187), has been held annually for 4 years and has attracted thousands of researchers and practitioners engaged in science, technology, engineering, mathematics, and computer science education. In a mixed methods study, we investigate the forms of participation that took place and the benefits that accrued to those who presented. We provide a thematic analysis of the textual discussions that took place, to further an understanding of the potential of a multimodal environments to facilitate rich collegial exchanges. Finally, the paper describes design decisions and embedded features that promoted different forms of interactivity among participants.