A one-system universe?
I posted a while ago about a "Star Fox" skin, and that gave me the idea a sufficient one-system universe could be emulated to the "Lylat" system which the game revolves around. I don't know the specifics, but it could have 1-2 suns, 6 plants, 8 nebulaes, and as many bases as the imagination can muster. No jump gates would be required.
Of course, that's just one strech of the imagination. I would imagine the one-system universe to contain any creative format someone can think of.