You want to challenge your friends in I, Gladiator...

But they have Linux or SteamOS...

Please tell your friends about our Kickstarter campaign, as backers they can gain even a beta access to I, Gladiator
https://www.kickstarter.com/projects/329567281/i-gladiator

BTW One of rewards gives you a legendary ingame Kolhid Sword! You can get a Kolhid Sword for yourself and present a Linux Steam key to your friend!!!