After reading some Planetary, references are made to other groups that apparently actually have written works (The Authority, S.T.O.R.M. Watch, etc.). After doing some more reading about the universe, it's a nice and confusing twist of ownership, imprints, and universes.
What comics officially share a universe with Planetary (both past and present, as I understand some things have been exchanged and made part of reboots and such)?