Starting today, Steam users can watch their friends games through Steam Broadcasting, which is now available in beta.
Valve said the new option will allow Steam users to click "Watch Game" on their friend's profile or via their friend's list.
This will open a window into said pal's gameplay, and "no game ownership, special fees, or additional apps" are required.
The beta is open to everyone who opts in to the Steam Client Beta, but note that at this time, bandwidth may be limited due to the beta.
You can find out more on Steam Broadcast through the update page.