Valve has announced Steam Family Sharing, a new service feature that "allows close friends and family members to share their libraries of Steam games."
The feature will become available next week, in limited beta and will allow others to play one another's Steam games while each earning their own Steam achievements and storing their own saves and application data to the Steam cloud.
It's all enabled by authorizing a shared computer.
"Our customers have expressed a desire to share their digital games among friends and family members, just as current retail games, books, DVDs, and other physical media can be shared," explained Anna Sweet of Valve. "Family Sharing was created in direct response to these user requests."
Once a device is authorized, the lender's library of Steam games becomes available for others on the machine to access, download, and play. 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.
Below is a Q&A on it sent over by Valve.
I want to try this! How can I join the Family Sharing Beta?
To express interest in beta participation, join the Family Sharing Group on the Steam community. The Family Sharing beta will begin in about a week, when a thousand Steam accounts from this group will be granted access to share their Steam libraries. You'll know you've been selected when you receive an email from Steam inviting you to try out the new feature.
How do I enable Family Sharing on my computer?
Family Sharing is enabled in one of two ways: You can either locally enable sharing in Account Settings, with Family Sharing & Devices, or remotely respond to a user's Steam request to share your previously installed games via email.
Is there a limit to the number of devices I can authorize to share my Library?
Yes. A Steam account may authorize Family Sharing on up to 10 devices at a given time.
Can I share specific games, or do I have to share my whole library?
Libraries are shared and borrowed in their entirety.
Can all Steam games be shared with friends and family?
No, due to technical limitations, some Steam games may be unavailable for sharing. For example, titles that require an additional third-party key, account, or subscription in order to play cannot be shared among friends and family.
Can a friend and I share a library and both play at the same time?
No, a shared library may only be accessed by one user at a time.
When I authorize a device to lend my library to others, do I limit my own ability to access and play my games?
As the lender, you may always access and play your games at any time. If you decide to start playing when a friend is already playing one of your games, he/she will be given a few minutes to either purchase the game or quit playing.
Sometimes the games I've borrowed are unavailable for me to play. Why?
Borrowed games are only available on computers that have been authorized by the lender. A borrowed game will not be available on a computer running an OS unsupported by that game. Borrowed games may also be unavailable if the lender's library is currently in use on another computer.
Who owns the DLC and in-game content associated with a borrowed title?
A borrower will have access to the lender's DLC, but borrowers may not purchase DLC for a base game they don't own. Any player may purchase, trade, earn, or otherwise acquire in-game content while playing a game, but in-game items cannot be shared between accounts. These items remain associated with the account that purchased or acquired them, whether borrowing or lending the base game.
Can region-restricted content be shared across regions?
No, any region restrictions will remain in place when borrowing or lending content.
Will I be punished for any cheating or fraud conducted by other users while playing my games?
Your Family Sharing privileges may be revoked if your library is used by borrowers to conduct cheating or fraud. We recommend you only authorize familiar computers you know to be secure.