Projekt Z will allow cross-play between 3 platforms

Projekt Z
Official Website: Link
Crossplay platforms:
Projekt Z will support cross-play across multiple platforms. It will be possible to play together with your friends on Windows PC, Linux and Google Stadia. Please check out all the details on the game's official website!
Cross-Platform Combination Details:
The release date is unknown.
Source: Link
Additional Info: Crossplay will work between the Steam Version of Linux/Windows and Google Stadia.
Summary:
"Projekt Z" is an atmospheric First-Person Zombie Co-Op-Shooter set in WW2. In this game, you get to play different characters, who have very different abilities, to find out more about the secrets of the german island you all crashed on.
Screenshots:
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