Only thing on the top of my head is Spore but that is terrible for what you want.
I too have been look one.
I have one: Universe Sandbox - It's really confusing but fun when you get into it.
Any luck then?Already tried the trial.I want one that focuses on planet creation, then development. Not a simulator that focuses on orbital bodies and collisions. Probably should have clarified that.
Universe Sandbox?
Already tried the trial.
http://kotaku.com/5616141/from-dust-is-for-those-of-you-who-like-playing-god
Is that going to be for PC?
Yes.
http://forums.funny-games.biz/planet-creator-t8415.html?s=7cae13ae5e6bd74b9656079b4dca1c8b&This is obviously what you were looking for.