Users have reported that X3: Terran Conflict, the space opera developed by the Egosoft studio, has starter working in Steam for Linux.
X3: Terran Conflict is a stand-alone title in the X3 Universe, originally released back on 2008, and it's the culmination of the X trilogy.
According to the developers, gamers can take on the roles of different characters in the X universe, or of a Terran military pilot, and experience a multitude of stories.
This is the second game from Egosoft released on Steam for Linux, after X3 Reunion was also made available. It's important to mention that both games have been ported to Linux long before Steam was announced for the open source platform.