From publisher blurb:

Written by ENWorld's own Adam Windsor (whose writing credits include contributions to Creature Collection III, The ENWorld Player's Journal, and ENWorld Story Hour forums under the name Capellan), this book contains all you'd every want to know about Hooked Hammers - and they're not just for Gnomes anymore, either!

These brutal weapons may have been of small size originally, but they pack a real whallop, and so does this latest offering in the ENArsenal series.

E.N. Arsenal books are "crunch-intensive" - a majority of the PDF is devoted to rules-based material regarding the topic of the book; in this case, the Hooked Hammer and variants. E.N. Arsenal- Hooked Hammer explores the hooked hammer with 23 pages of material about the weapon itself, variants thereof, and those who wield them.

This e-book includes:

Statistics for hooked hammers of Fine through Colossal size.
9 variants of the hooked hammer and five weaponcrafting enhancements.
Tricks, Tactics and Techniques, including 12 Feats for the wielders of these tricky weapons.
Three prestige classes (and one psionic variant) dedicated to the weapon.
Spells
Weapon Enhancements for crafting magical hooked hammers.
Arbran Gemshine, god of Jewels and Artifice, whose favoured weapon is the hooked hammer- includes the Jewel and Artifice domains.