Flipgrid is an excellent video-based discussion platform that allows teachers and students (and parents) to engage in rich and interactive learning. The way Flipgrid works is simple and easy. As a teacher you can choose a topic you want to discuss with your students and post discussion prompts to which students reply using short video clips. You can also invite guests to join your discussion community. Participants can comment on each others entries and exchange feedback. If you run out of topic ideas, Flipgrid offers thousands of lessons, educational activities, and topic ideas to get you inspired.
Kahoot functions more or less like Flipgrid. It also provides you with a platform where you can conduct formative assessments through live interactive discussions and learning games. You can create a kahoot for your class and invite your students to join discussion. You can add various types of questions to your kahoot, import slides, import spreadsheets, and many more.