• Muddiest Point: At any time, students can be asked “what was the muddiest point in the (lecture, homework, reading ,etc)”? and given time to respond. This is a common 'exit ticket' activity that can also be adapted for discussions:
  • Conduct 'muddiest point parties' in breakout rooms. Give groups a set time in which to discuss their muddiest points and to help one another to clarify their understanding.  While in breakouts, one person should record a list of the points discussed (and even share them with the instructor via a tracking document). When all groups come back to the main room, one student from each will ‘report’ on what their muddiest points were, and ask questions still needing clarification.
• Comprehension check: Throughout a lecture, the instructor regularly displays a problem and gives students time to work through it independently. The question could be given on a slide, on the zoom whiteboard, or via a polling tool. Their responses will give you a sense of whether a particular problem or concept needs more explanation and practice.
• Group Problem Solving: In breakout rooms, students engage with a set of problems assigned by the instructor, and use the 'ask for help' button as needed to request the instructor join them in the room to provide help. 
• Alone-Together (with instructor): Students can work independently (either while still in the main zoom room, with their mic muted, or the instructor can assign each student to their own personal breakout room where they can work and seek individual help from the instructor via the "ask for help" button. After a set time, the instructor can ask students to join group breakout rooms to discuss the work they've done and compare notes. 
• Alone-Together (no instructor): Have students spend the first section of class time alone, offline, completing  an activity. After a set time (30 minutes, for example) students join a small group of classmates for student-driven discussion and collaboration on a new assignment that is directly based on the individual activity they just completed. During their collaborative time, students document their work or discussion, in detail, and submit it to the instructor. with thanks to Liza Flood, PhD
• Defined Discussions: many faculty have found that online discussion activities require more setup and structure. For an online discussion, define roles such as convener (to spark conversation), discussant (to ask follow-up questions), devil's advocate, recorder (to record and report either in-real-time or following the activity), etc. Set time limits and use "broadcast message" feature to remind students of the time. 
• Debates: consider using breakouts or holding a 'Fishbowl' debate in which two teams of students debate actively while other students observe and reflect (including a written reflection or post-debate discussion).

• Note Sharing: it is possible for multiple people to share screens at once (learn more about sharing multiple screens). Students can join breakout rooms and share their screens to review each other's notes on a topic to expand their understanding and correct inconsistencies.

Small group activities for Zoom breakout rooms (Stanford Teaching Commons) 

Active Learning in Hybrid and Physically-Distanced Classrooms (Vanderbilt Center for Teaching and Learning)

Active learning while physically distancing (Louisiana State University)