Caracal Games, the developers of the 1st-Person-Parkour game Downward, have kept word:

the Linux-version of Downward is now available on Steam!

Hint: only today you can still get it in the sale for 25% off!

Description:

Downward is a first-person open-world parkour adventure set in the medieval ruins of a post-apocalyptic Planet Earth. You must master body, mind, and spirit -- for agility, precision, and determination are the only tools that will help you make sense of this world and change your fate...