FreeOrion is described as 'Turn-based space empire and galactic conquest (4X) computer game being designed and built by the FreeOrion project. FreeOrion is inspired by the tradition of the Master of Orion games, but is not a clone or remake of that series or any other game' and is an game in the games category. There are more than 10 games similar to FreeOrion for a variety of platforms, including Windows, Steam, Linux, Space Empires IV Deluxe and Mac apps. The best FreeOrion alternative is Endless Space. It's not free, so if you're looking for a free alternative, you could try Open Realm of Stars or Cosmic Supremacy. Other FreeOrion like games are Stellaris, Galactic Civilizations, Space Empires IV Deluxe and Stellar Monarch.
Simple, fast, but in-depth. Clean and easy to understand inter phase. Great space 4x