YouTube is the most well-known video service on the Internet. YouTube lets anyone share videos online, either from their hard drive or recorded using their computer's Web cam. It uses Adobe Flash and a simple video player that starts playing videos right away.
YouTube has paved the way for a variety of other services and evolved its own services with new features such as user profiles, video rankings, and a system that lets anyone reply to a video either with text or another video. It's also introduced some controversial features such as video viewing history, and displaying who's watching a video at the same time you are.
In the past year, YouTube's rolled out high-definition video, a completely redesigned homepage, and a tool that tracks what you're watching and shares it with others in real-time. The site is also rumored to have a live video service in the works.