Valve released its Steam Family Options in January, but has just now unshackled Steam Family Sharing from its long-standing beta run, making it available to all Steam users.
If you haven't heard of Steam Family Sharing until now, let's run through it. Steam Family Sharing allows those with blood ties to you to freely share access to retail PC, Mac and Linux game releases through Steam. Valve's official description of Steam Family Sharing reads: "Players who share computers can now also share their available libraries with one another, each earning their own achievements and saving their own game progress to the Steam Cloud. It's all enabled by authorizing shared computers and the familiar accounts that log into them".