Appear.in is a free service that allows you to screenshare with others and have video chats with several people. You simply share the link to your chat with the people you are inviting. If you want to make the room private, you can lock the room. It does not require the download of software, a plus if you are working on a Chromebook.
It doesn’t record the conversation, so it wouldn’t be useful for a flipped classroom scenario, but it would come in handy for collaborating with others in real-time.
Students can use appear.in to make online study groups, connect with friends that have moved away, bring guest speakers to the class, etc.