Platforms: PC, Mac, Linux
Price: $26.99 (currently on sale for $18.08 on Steam)
A lot of games use space as a setting and more often than not, it's used as a means to implement alien races and dogfights and other sci-fi elements. Few games present space as a frontier to be explored; the only one I can think of is Outer Wilds. Like that game, Kerbal Space Program offers the player an open universe to explore, but while Outer Wilds was all about discovery, Kerbal takes the physics-heavy technical approach and turns space exploration into a thrilling scientific experience.
developer's site and Steam.