Steam is officially available on a handful of Chromebooks

engadget.com:

A week ago, Google somewhat surprisingly announced that Steam was coming to Chromebooks in a very early alpha test format — but aside from a mention of this during the company's Games Developer Summit keynote, there were no details to be had. Given the somewhat surprising amount of interest around it, Google is now making things a bit more official by releasing instructions on how to get Steam up and running on Chrome OS. The company is also providing details on supported hardware, games that should work and bugs you can expect to run into. 

For starters, you'll need a supported device, and it's only a handful of Chromebooks. Google says that you'll need a device with Intel Iris Xe Graphics, 11th-generation Core i5 or i7 processors and at least 8GB of RAM. Google specifically said that configurations with an Intel i3 processor or 4GB of RAM aren't supported. For the alpha, only the following devices are supported:

●  Acer Chromebook 514 (CB514-1W)

●  Acer Chromebook 515 (CB515-1W)

●  Acer Chromebook Spin 713 (CP713-3W)

●  ASUS Chromebook Flip CX5 (CX5500)

●  ASUS Chromebook CX9 (CX9400)

●  HP Pro c640 G2 Chromebook

●  Lenovo 5i-14 Chromebook

Assuming you have supported hardware, Google says you'll need to switch your Chromebook to the Dev channel, and cautions that you shouldn't do this with hardware that you rely on for daily use. From there, you'll need to enable a specific flag in Chrome as well as type a few commands into Chrome OS's Crosh terminal. Google says you can find full directions here.

Once you have Steam installed, there's a surprisingly large group of games that Google has tried and suggests testers try as well. Unsurprisingly, it includes a lot of Valve titles like Portal 2, Dota 2, Team Fortress 2 and Half-Life