Big Blue Button is a tool for synchronous audio/video discussions. It integrates with Moodle, Mattermost and even has stand-alone access via the Greenlight front end. It includes video-based chat, whiteboard, session-recording and screen sharing functionality.
Use it when you want to interact with others in real-time and save recordings for later. It is great for computer-based instruction at a distance, but is not a classroom-based lecture broadcast/capture system.