Sharing of games with up to 10 other users is now possible through Steam Family Sharing. After establishing a request to access a friend’s game library, one can acquire access to all the games on the computer provided they attain authorization. This would allow users to earn their own Steam achievements and save their own progress to the Steam Cloud.
Steam Family sharing is in beta now, which will means that members can express interest in the beta only by joining the family Sharing group.
While the owner of the library can access his collection at all times, only one user is legally allowed to access the library at a time. Also, if a third person is involved in playing the game in the library, the friend has an option of either buying the game or quitting.
Sharing would not be allowed with games that need a third-party key, account or subscription. Sharing would allow access to the DLC of the library’s owner, but friends will not be allowed to purchase the DLC unless they own the base game as well. Region based restrictions on games however have not been altered yet.