Noctis is a space-exploration simulator, containing a massive, randomly-generated universe. It is single-player, and used to be pseudo-multiplayer - you could assign planets and stars names in the Guide, and list descriptions of them, then send the data out to be updated on all copies of the game. That function no longer really exists; my planet names will stay in my game.
A ringed world in Noctis
A volcanic world in Noctis
A living world in Noctis
I highly recommend Noctis. It's old, but the joy of discovering worlds and views that no-one else has ever seen is still there. The planned-for-2016 game No Man's Sky looks like it might replicate the key components of that (vast galaxy, named by users, but still single-player), but until we find out, Noctis stands alone.
Years ago, I wrote a survey report for a triple star system in Noctis, Isis/Osiris/Set. I never finished it. Rather than do the sensible thing and work through it to the end, I started fresh and wrote a new one: