Today Valve unveiled their new Family Sharing service on Steam. The service will allow you to share the majority of your game library with relatives and close friends.
There are a few limitations however. You can only share your games across 10 devices, and if someone is playing one of your games they’ll be prompted to either buy the game or exit out of it when you load something in the library. It’s also mentioned on the page that games which require third party accounts or keys will likely not be able to be shared on the service.
The Beta for the service isn’t dated yet, instead it is simply listed as “coming soon”. If you want to get yourself jammed into that beta ASAP you can follow this link.