Fallen Moon is the D&D setting for all your moon-crashing-into-the-planet-but-a-few-people-survive-and-need-to-work-together-despite-the-fact-that-some-of-them-hate-each-other needs.
With a focus on a dangerous wasteland riddled with Undead, populated with a few aliens, including the last city standing in the world, and the moon itself, this world is ready for adventure! So ready it might be hard to pick where to start!
In Fallen Moon, you might...
Where should you go first, you ask? The Convenience and Rules article provides an overview of this setting.