Steam Family Sharing
 

http://store.steampowered.com/sharing

Steam Family Sharing, a new service feature that allows close friends and family members to share their libraries of Steam games, is coming to Steam

Though simultaneous usage of an account’s library is not allowed, the lender may always access and play his games at any time. If he decides to start playing when a friend is borrowing one of his games, the friend will be given a few minutes to either purchase the game or quit playing.

The Family Sharing beta will begin in mid-September
A Steam account may authorize Family Sharing on up to 10 devices at a given time.

Re: Steam Family Sharing
 

Seems nifty

Re: Steam Family Sharing
 

See this is why Steam is awesome.