Re: Anyone else remember the 'Spelljammer' campaign setting?
Hell yeah I remember it fondly! I started playing with 2nd Edition and loved all of the campaign settings, and they definitely had some strange ones. Planescape was my favorite, but Spelljammer and Dark Sun were in the running for 2nd and 3rd. They were weird settings, not much like the 'regular' fantasy ones like Greyhawk or Forgotten Realms. Spelljammer was definitely the most unusual of them all, though...and some of the products had some inconsistent writing, and lore that didn't mesh well with previously established lore.
It had Large Luigi, the Beholder bartender that knew he was an NPC in a game. It had Falx, the planet where herds of Tarrasques roamed. Astromundi Cluster tried to make an origin story for Illithids that completely forgot all about the Far Realm, the Illithid Empire, the Gith, etc. Also hippo-people with guns (the Giff). The Xixchil, those thri-kreen cousins who loved performing surgery on people. "You asked for the eyes of an eagle, the beak and feathers were free!" And don't forget giant mutant space hamsters.
It was all fun, though.
As for cosmology... You have the Prime Material Plane, which is composed of Chrystal Spheres. Phlogiston fills the gap between the spheres and only Spelljamming vessels can travel through Phlogiston. You then have the Inner Planes and the Outer Planes. Inner Planes (4 Elemental, 4 Para-elemental, 8 Quasi-elemental, and 2 energy planes) are connected to the Prime by the Ethereal Plane. The Outer Planes (Hell/Baator, Heaven/Mt. Celestia, The Abyss, etc.) are connected to the Prime via the Astral Plane. Neither Astral nor Ethereal connect to the Phlogiston, so the Phlogiston is the only place on the Prime not connected to any other planes. Demi-Planes, like Ravenloft, are part of the Ethereal Plane.
All the other settings had their own Crystal Spheres, and theoretically our modern Earth was somewhere out there as well.