From the back cover:
They are the four-horned Feathered Fowl, once great champions of a god lost to memory. Now, they have been turned against him and bound to serve as jailors of a divine prison. Straining against the confines of their Oaths, they scour the multiverse seeking the 'greatest of the grand,' ripping them from their homes and bringing them to the Forge.
Domains of the Forge
The divine power of the trapped god seeps into the land and its heroes, imbuing them with great powers and abilities. Unique prestige classes give insight into the world's mysteries and allow heroes to thrive within its borders, leaving them forever changed.
A countless wealth of races, cultures, magic, and knowledge has been pulled to the land from millions of other worlds, woven into a unique tapestry that is the Forge. You will be forever altered.