Valve's Steam Family Sharing beta system has expired and is now in fully release.
Lenders can authorize up to 10 computer devices and 5 accounts, but there is a catch: Should the primary user log onto a game, anyone else using it will be either bumped off or forced to pay. Should they opt for the latter, their game stats or progress is carried over and saved in Steam Cloud.
How to share your games
To share your library of games with friends and family, you need to enable the feature by doing the following:
1. Open Steam interface
2. On the Steam menu, go to Settings menu item
3. On the appearing popup, go to Family on the left
4. Authorize specific users and computers
For close friends and families
When Valve launched the beta last fall, it stressed the second bit of Steam Family Sharing, saying the system is for family and close friends only.
Valve reported that some games are not sharable through the Steam Family Sharing for the reason that it might require an account or subscription. Also, no two players can play the same game at the same time.