Dadie Piombo has a set of basic rules for playing Pulp Action miniatures games.
rules
Steve’s Horse and Musket Rules
Steve’s Horse and Musket Rules are designed to be a simple set of rules emphasizing the three arms (horse, foot, guns) and command.
American Civil War Riverine Actions
Mike Callan offers this set of free wargames rules for American Civil War Ironclads. The set originally was published in Wargames Illustrated 14.
Trireme Ancient Naval Rules
Trireme, from Andy Watkins, is a set of free naval wargames rules. These are of the one-page variety, which means that there is much to recommend them. I also like the staggered movement system based on boat speed, which reminds me of the old Car Wars system.
BloodBowl Hockey Variant
Here’s a variant for Games Workshop’s BloodBowl Game in a hockey format.