tl;dr: PeerTube is an AGPL-licensed, federated video platform from Framasoft that uses ActivityPub to interoperate with the Fediverse (Mastodon, Pleroma, etc.) and WebRTC for peer-to-peer load sharing between viewers. It supports both on-demand and live streaming, lets instances cache each other's videos for redundancy, and offers creator support via donation links rather than ads or recommendation algorithms. Anyone can self-host an instance or join an existing one, with no vendor lock-in.