Justin.tv is a live video streaming service. It began with founder Justin Kan who wandered around the streets of San Francisco with a Web cam that was hooked up to a laptop in his backpack. That was connected to EV-DO card that was streaming everything he was doing live to everyone through the Justin.tv platform.
Following that trial run, Justin.tv was opened up to others who wanted their own channels, and eventually to everyone. It's now a large live streaming network that also keeps archives of everything that's streamed online. Each video room includes live chat, and simple ways to share the live and archived content, either on blogs or social-networking sites.