https://www.techradar.com/news/steam-machines-running-windows-games-valves-working-on-it

Back in April, game maker and online retailer Valve promised that it wasn’t finished with its Steam Machine PC gaming platform, determined to create the alternative to Microsoft’s Windows. Now, Valve has found a shortcut: emulating Windows games.

Clever Reddit users have uncovered within the Steam client’s graphical user interface files, via a ‘Steam Tracker’ through the GitHub open source code base, references to an unannounced ‘Steam Play’ system for essentially emulating games that weren’t built for Valve’s own Linux-based SteamOS operating system (OS), ArsTechnica reports.