today that Steam's Family Library Sharing system is now available to all Steam users.
The game lending system was first announced
in September of last year and has been available to select beta testers for months.
Now that it's live, all Steam users can share games in their Steam libraries with up to five other Steam accounts across up to ten different computers by activating the sharing feature in Steam's Family Library Sharing settings menu. Steam Achievements and Steam Cloud save data are tracked separately for each user, regardless of which libraries they're borrowing from.
Only one person may play games from a given library at a time, and if two users attempt to play from the same library simultaneously the borrowing player will be prompted to either quit their current game or buy a separate copy.
The Family Sharing feature does not allow users to circumvent region-based restrictions or play games that require third-party keys or subscriptions. For more details, check out the FAQ
published on the Steam website.