StarMade is as much a game as it is a universe/planet/spaceship building simulation. Whole planets can be created, as well as whole universes, both in single and multi player, and players can then build ships to fly around in and interact with this universe.
"StarMade is a voxel-based 3D sandbox space shooter. Play in your own universe or on a multiplayer server to create, discover, destroy, customize, and design your own worlds." - Official Site