Battle for Orion 2 [Steam, Official Site], not to be confused with Master of Orion 2, a game that mixes galactic domination with real time strategy has a Linux version.

The game was released for Windows back in March, but in May they released the Linux version! It seems it was missed, since it wouldn't have shown up in Steam's newly released for Linux list. Hopefully one day Valve will sort that out, it's sad that so many games are likely still being missed when they add a Linux version later.

This is the second game from Infinite Loop Games, the first was the prequel which was a mobile game. So it seems like this is their first PC release.

Features:

Galactic domination meets real time strategy

Battle through 24 story missions that will challenge and engage you

Conquer star systems to expand your empire and control of the galaxy

Construct orbital modules around planets to improve your economy, military, and research

Mine asteroids, space debris, and moons for resources

Build over a dozen unique ships including capitol ships with advanced abilities

Collect powerful technology to strengthen your fleet, economy, and defenses

Build massive superweapons powered by stars

Randomly generate endless maps with the Battle Simulator

Create your own galaxy and publish maps for other players to enjoy with the built in Map Editor

I've requested a review key from the developer, as it sounds like something I would enjoy giving it a go. Hopefully we will be able to review it for you.