Gangs of Skavenblight is an Warhammer Fantasy adaptation of Footsore Miniatures’ Gangs of Rome Game. It features, as you might imagine, gangs of Skaven fighting for control of the city of the Horned Rat.
All of the links below are to pdf files.
Games Workshop offers a free pdf of its Warhammer 40K battle primer, which contains basic for moving, shooting, fighting, using psychic powers and morale, along with other material to get you started.
Epic Escarmouches is an original wargames rules system based on Space Marine and Epic 40K.
Warhammer French and Indian War is a set of free wargames rules based on the Warhammer English Civil War rules.