Sometimes the games I've been given access to are unavailable for me to play. Why? Shared games are only available on devices that have been authorized by the account holder. Shared games will be unavailable on even an authorized device when the account holder's library is currently in use on another computer.

Requesting access from owner: Be sure to enable Steam Guard on your Steam Account. From your Library you'll be able to see games owned by other Steam accounts that use the same computer. Select a game and click "Borrow" to request access to that respective Library.

Any two computers connected to Steam can be used to stream a gameplay session and this can enable playing games on systems that would not traditionally be able to run those games. For example, a Windows only game could be streamed from a Windows PC to a Steam Machine running Linux in the living room.

Sometimes, we take the servers down in order to perform maintenance. We might be patching software for security issues, updating operating systems or drivers, or installing new hardware, for example. These activities don't result in new features, but allow Steam to continue to run stably and efficiently.