Star Citizen is described as 'Space sim video game for Microsoft Windows. Star Citizen is planned to consist of two main components: first-person space combat, mining, exploration and trading with first-person shooter elements in a massively multiplayer persistent universe and customizable' and is a role-playing game in the games category. There are more than 10 games similar to Star Citizen for a variety of platforms, including Windows, Steam, Mac, Linux and Xbox apps. The best Star Citizen 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 Star Citizen like games are Qanga, Elite: Dangerous, Starsector and Starfield.
All you do is fly around procedurally generated planets and scan/mine stuff to upgrade your ship. No role-playing, very little if any combat, and no spaceports or cities to visit.