Steam Broadcasting is now live following the latest update to the Steam Client, it was announced today.
The new broadcasting feature allows users to watch and stream games to and from users on your friends list. Right-clicking the name of a friend who's in-game now offers the option to "Watch Game." Clicking this will send a request, which needs to be accepted before viewing can start. The feature also includes a chat that can be seen by the player.
Steam Broadcasting was first announced late last year as a planned alternative to third-party streaming services like Twitch and Ustream.
Valve described Steam's new broadcasting feature as being "designed for ease of use, allowing anyone to view a friend's game by simply clicking on 'Watch Game' on their Friend's profile or Friend's List to open a window into their gameplay - no game ownership, special fees, or additional apps required."
Additional changes to the Steam Client can be found here, including a frames-per-second counter.