Here’s a set of classic wargames rules from 1969: Charles Sweet’s American Revolution rules.
Miniatures Rules
Regiments and Roundshot Napoleonic Miniatures Rules
Regiments and Roundshot is a set of very simple Napoleonics rules. Interestingly, the instructions call for using a white board for terrain.
Wrath of Kings Fantasy Rules
Wrath of Kings is a set of demo rules for a fantasy skirmish system. It has some interesting concepts.
Indian Mutiny 1857
Indian Mutiny 1857 is a set of skirmish wargames rules for the Indian Mutiny.
Ironclad American Civil War Naval Rules
From the Naval Wargames Association comes Ironclad, a set of free wargames rules for ACW ironclads.