tl;dr: PeerTube is an open-source, federated video platform from Framasoft that uses ActivityPub to interoperate with the Fediverse (Mastodon, Pleroma, etc.) and WebRTC for peer-to-peer streaming to reduce bandwidth costs. It supports both video-on-demand and live streaming, lets instances cache each other's content for redundancy, and offers creator support via donation links rather than ads or recommendation algorithms. Anyone can self-host an instance, and users can follow channels across instances without needing accounts on each.