Croteam, the Croatian-based game development studio behind the Serious Sam series, proudly posted a couple of days ago, July 18th, on their Facebook page, a screenshot of Serious Sam 3 running on Ubuntu Linux distribution.
There are no other details, besides the screenshot (click it above to enlarge) posted on Facebook by Croteam. Apparently the game was ported to the Linux platform and tested on the Ubuntu operating system.
Released eight months ago, on November 22nd 2011, the third iteration in the Serious Sam series, Serious Sam 3: BFE (Before First Encounter), is a first-person shooter (FPS) video game developed by Croteam and published by Devolver Digital. It is the prequel to Serious Sam: The First Encounter.
Looks to me like more and more developers bring their games to users of the open source Linux platform. We'll wait now for the release of Valve's Steam client, in fall 2012, and we will inform you want Serious Sam 3 is available for purchase on the Linux platform.