Valve has announced a Steam Link app for iOS and Android tablets and smartphones, which will allow people to play their PC games o their mobile devices. As long as you are connected via 5Ghz network or wired Ethernet to a host system (Mac or PC), you will be able to stream your PC games to your smart device.
While a lot of PC games are’t all that well suited for something like this, things like Civilization, XCOM, Total War, sim games, and visual novels- all of which there are a lot of on Steam- would be ideally suited for something like this. It’s an excellent initiative, and I can see a lot of use for something like this (I would love to play Civilization 5 on my iPad, as an example).
Only Android access will initially be offered in beta, but I am sure wider release should be coming shortly.