I have been looking around at the open-source solutions to self-host your own web conferences as an alternative to commercial solutions. I first looked at Big Blue Button and later discovered the project Jitsi. Both offer screen sharing, audio/video/webcam sharing, external videos, public/private chat, and emoticons. Jitsi supports multiple screen shares while BBB supports document upload, whiteboards, polling and breakout rooms. BBB recommends Ubuntu 16.04 and a beefy server, while Jitsi runs on Ubuntu 18.