Co-op: four teams, four planets, four completely separate tech trees. Every team starts from nothing on its own planet - Nauvis, Vulcanus, Fulgora or Gleba - and must independently research the ENTIRE tech tree using only what that planet provides. No shared research, no imports, no help from the others. A team only stops being alone when it researches its planet's discovery technology, which now costs that planet's own science pack. That merges it into a shared unified force which accumulates every discovery so far - and only then does anyone get thrusters and interplanetary travel. Until a planet has been mastered, nobody leaves its orbit. Play it with friends, one planet each, or solo by hopping between teams and running all four yourself.
Mods introducing new content into the game.