This research memorandum describes the development and operation of an extension to Open edX (XBlock) called CPSX, designed to enable small-group synchronous discussion alongside any instructional or assessment media in the Open edX platform. The CPSX XBlock provides a size-limited chat session to content authors as one of the elements of a typical course unit. Chat transcripts are stored using the same MySQL server as the Open edX instance. This work was supported by the Center for Academic and Workforce Readiness and Success to enable simple experiments on collaborative performance; however, the tool is fully usable as an instructional affordance in online courses built using Open edX.