Huge fan of luanti (minetest) as well. My kids never picked it up though because the client controls were not very polished and they got frustrated. Has that improved in the years?
Well, that's configurable. On full games, you just download them from the manager and start a new world with that game in the main menu. For instance, "Glitch" has nothing to do with "NodeCore", nor Mineclonia or Citadel.