Valve wants as many gamers as possible able to play titles from the Steam store, which is why for the past eight years buying a Steam game meant getting Windows, Mac, and Linux versions if they were available. This is called Steam Play, and it just received a major overhaul to open up thousands more games to Linux.
Linux users typically lose out when it comes to gaming as the vast majority of titles are developed for the most popular platform, which has always been Windows. A Linux version provided by the developer is a bonus, but now the lack of a Linux version doesn't stop it being played on a Linux gaming rig thanks to Valve.
In a post on Steam, Valve announced a new version of Steam Play that includes a modified version of Wine called Proton. Wine is a compatibility layer used on Linux to run Windows applications. Valve took Wine, supported it, and integrated it into Steam as Proton. The end result being Windows-only games can now be played on Linux using Proton.
Valve also added support for the Vulkan graphics API, which allows for improved DirectX 11 and 12 game compatibility on Linux as well as a reduced impact on game performance. Fullscreen support has also been enhanced, as has controller support and multi-threaded game performance when playing on the alternative OS.
For now, this new version of Steam Play is being released in beta form, but it does add support for 27 games including Doom, Final Fantasy VI, Quake, and Star Wars: Battlefront 2 to name just a few. More games will be added as Valve's testing process continues, with the goal being to get all games within the Steam library working.
Valve readily admits some games may never work, but that's down to the DRM and anti-cheat software used rather than the games themselves refusing to run. And right now the beta will allow you to try games that aren't marked as compatible yet, so your favorite "I can't play it on Linux" title may now just work!