From the back of the book:
AN EVENT BOOK by BRUCE R. CORDELL
Shake Up Your Campaign!
The sky burns with shooting stars. When some of them hit the ground, the very earth trembles—and horrifying new creatures and potent magic arise.
This event book serves as a guide for DMs and players whose world is struck—and struck hard—by a meteor.When the Sky Falls offers a variety of new prestige classes for characters close to the impact, a variant magic system powered by residual meteor fragments, and many new feats, spells, and items. The book also describes frightening new monsters: creatures twisted by their proximity to the Afterfall.