They have contributed to the Wine project for some time and will incorporate a modified wine in their gaming platform called Proton.
So, two years ago, we started an effort to improve the quality and performance of Windows compatibility solutions for Steam games. A lot of our work has been in the form of supporting Wine[www.winehq.org] and other existing compatibility projects. We have also been integrating these tools into the Steam client to provide the same simple plug-and-play experience offered by regular Linux games.
Furthermore steam encourages the development for for the Linux platform.
ATM the following titles are working on Linux:
- Beat Saber
Bejeweled 2 Deluxe
Doki Doki Literature Club!
DOOM II: Hell on Earth
FINAL FANTASY VI
Google Earth VR
Into The Breach
Magic: The Gathering - Duels of the Planeswalkers 2012
Magic: The Gathering - Duels of the Planeswalkers 2013
Mount & Blade
Mount & Blade: With Fire & Sword
PAYDAY: The Heist
S.T.A.L.K.E.R.: Shadow of Chernobyl
Star Wars: Battlefront 2
The Last Remnant
Warhammer® 40,000: Dawn of War® - Dark Crusade
Warhammer® 40,000: Dawn of War® - Soulstorm
I have been playing Team Fortress on Manjaro Linux for years so I know that these titles are not all that Linux can handle.
Looks like the future of gaming belongs to Linux since Steam is clearly the biggest gaming company out there.