Starfield is described as 'The first new universe in 25 years from Bethesda Game Studios, the award-winning creators of The Elder Scrolls V: Skyrim and Fallout 4. In this next generation role-playing game set amongst the stars, embark on an epic journey to answer humanity’s greatest mystery' and is a Open World Game in the games category. There are more than 10 games similar to Starfield for a variety of platforms, including Windows, Steam, Linux, Mac and Xbox apps. The best Starfield alternative is No Man's Sky. It's not free, so if you're looking for a free alternative, you could try EVE Online or AstroImpact. Other Starfield like games are Space Engine, Qanga, Star Citizen and Starbound.
Same enviroment, same exploration, but multiplayer, more randomness, survival, sandbox, more flying. Less story and worse graphic tho.