Open source alternatives to agora.io for real-time communication

I am the founder of an ed-tech platform. We conduct live classes where the trainer streams to a set of students with an option to post text comments/questions during the live class (visible to everyone). We also record these sessions and provide them to our students. Currently, we are using Agora for this. But being a bootstrapped startup, the charges are very unsustainable. Is there a FOSS alternative that's easy to implement without having to hire WebRTC developers?