Valve has finished beta testing the Steam Family Sharing feature and has now made it available to all Steam users.
As the name suggests, the feature allows users to share their game libraries with friends and family. There are a few caveats, though: You can only share titles that do not need an additional third party key, account, or subscription in order to play the game. Also, you cannot choose selective titles to share in your game library. When you share your game library with a friend or family member, your entire collection of games will be shared.