Steam has just made a very cool announcement–they will be introducing Family Sharing, which will allow close friends and family members to play one another’s games while earning their own Steam achievements and saving their own game progress to the Steam cloud. This feature will be enabled by authorizing a shared PC.
According to the official site, the feature works like this: if you see an installed game you want to play, send the family member/friend a request to authorize the computer. Once authorized, the lender’s library of Steam games become available for others on the PC to access, download and play.
The beta will commence soon for the service and you can join the group to express interest in it by going here. You can also use the link above to access the FAQ and the site’s group discussions.