In-Home Streaming is now an option for everybody with a Steam account, as the system is out of open beta and fully released today. Streaming allows you to use a more powerful device (a desktop PC with a beefy graphics card, say) to stream a game to a less powerful one (maybe an older laptop,) or to a device running an operating system the game wouldn’t normally get along with.
Setting it up to have a go is pretty straightforward. You just need to log in to Steam on the PC you’re planning to stream from, log in to Steam on another device on the same network (that you wish to stream to) and then visit your Steam library on the second device. It should give you the option to begin streaming the games you have installed.
When I gave this system a try a few months back it was still in beta, but coped relatively well in imperfect conditions (streaming to a really old laptop, and over a wireless connection between a couple of rooms.) By most accounts streaming has only improved since then, so it’s well worth trying even if you don’t think your conditions will be ideal for it.
You can read a few more things about In-Home Streaming over here on Valve’s page.