Steam is a digital distribution platform developed by Valve Corporation for purchasing and playing video games that was first launched in 2003 for Windows computer only.
Since then Mac OS (2010), Linux / Ubuntu, as well as mobile devices running Android & iOS (2012) have been supported in Steam. Mobile could only be used to browse the storefront, manage games, and access the community.
However more recently, the company released Steam Link app that allows players to stream games to their mobile devices, while being rendering on more powerful machines. The good news is that Steam Link (beta) has now been released for Raspberry Pi 3 / 3B + boards.
All you need is either board running Raspbian Stretch, and install Steam Link as follows:
curl -#Of http://media.steampowered.com/steamlink/rpi/steamlink_1.0.5_armhf.deb
sudo dpkg -i steamlink_1.0.5_armhf.deb
Once the app is installed launch it in the command line with steamlink, or launch it from the Games menu in the desktop environment.
Steam Link support has already been added to RetroPie, and ETA PRIME took it for a spin in the video below.
Thanks to Harley for the tip.