The Kalevala is compiled works of finnish folklore and poetry. It tells tales of northern heroes (male and female), artifacts, magic, supernatural, love, war, music, folklore, ancient gods, history, finnish stubborness and bravery. Sometimes story takes almoust epic portions involving powerful, almoust god-like, finnish heroes. It is major source of finnish mythology and paganism also.
For more information and details about subject, please check Wikipedia: Kalevala
So, what is Kalevala Hammer then? Well, including the name of the site, the hammer is not anyway part Kalevala mythology. It is actually mysterious and famous Norscan artifact forged by Norse Dwarf Runesmith. It was originally reward for Norse hero, who became Dwarf-friend. More info can be found from Rune Magic Expansion -page (as well as Timeline: Norsca -page and Norsca: Religion -document).