In August of 2018 Valve released an official method for downloading and playing games originally meant for Windows on GNU/Linux. You can read the announcement here.
They integrated Wine into Steam and called it Proton.
By default, if you are on GNU/Linux, Steam will allow you to download and play a few whitelisted games that only have builds for Windows. On release, Steam Play for GNU/Linux came with 27 whitelisted games. As of 2019-08-04 Valve seem to have whitelisted 168 titles.
There's no official list of whitelisted games from Valve, but SteamDB offers a list here.
However, if you are feeling adventurous, there's an option in Steam to enable Steam Play for all Windows only titles in your library!
Here's how to do it:
- Open Steam and navigate to Settings
- In the account tab, click 'beta participation' and opt in for the 'Steam Beta Update' selection in the drop down menu.
- Once you save the settings (hit 'OK'), Steam will restart and download the new beta updates.
- When it's done, go back into Settings, select the 'Steam Play' tab and check 'Enable Steam Play for all titles'.
- Done! You can now try to run any title that previously was Windows only on GNU/Linux! These Windows only titles will now say 'Run on this computer via Steam Play' when selected in your Steam library. It's as simple as Install and Play!
There's a catch though, as a lot of games still have a long way to go when it comes to working properly under Wine/Proton - hence why they are unsupported - but Wine gets better every year, and Valve keep whitelisting games.
To check user reports on an unofficially supported game you'd like to try running with Steam Play on GNU/Linux, check out ProtonDB, an unofficial fan site where users report what success or failure they have trying to run unsupported games with Steam Play.