SpaceEngine

SpaceEngine from Cosmographic Software is a 1:1-scale science-based universe simulator — not a game, exactly, but the most accurate explorable cosmos available on PC. Billions of galaxies, nebulae, stars, and planets all rendered at real-world astronomical scale, transitioning seamlessly from a moon's surface to interstellar space to galaxy cluster scale with no loading screens. Where SpaceEngine has actual catalog data (real galaxies, stars, exoplanets, our Solar System) it uses it; where data doesn't exist, it generates plausible procedural worlds following physical models.

It's the planetarium that astronomy professors use as a teaching tool. Spacecraft physics simulation, orbital mechanics, ship design tools, and a relativistic warp-drive flight model are layered on top, so you can pilot custom-designed spacecraft between stars in real time or accelerated time. Cosmographic Software has been patching it for years; this is build 21042159.

Released with CSF + Goldberg, fully offline-playable. 54 GB installed (much of which is texture caches and astronomical catalog data). Single-player only. Steam Workshop is not reachable from cracked builds; community-built spacecraft and missions can be installed manually from forum downloads.