The MAWs offer a set of free wargames rules for the French and Indian War using 54mm figures.
Designed for kids, the No Dice Dark Age Rules fit on just three pages and use playing cards for resolution.
Pike And Shot is John Armatys’ set of free wargames rules for fighting battles of the English Civil War. The rules also can be used to resolve battles of other 17th Century Western European conflicts. The rules set appears designed for 15mm figures, but has special instructions for using 25mm figs.
Trench Raider is a set of free wargames rules for WWI trench warfare.
Charge of the Light Brigade is a set of free wargames rules by David Raybin for mid-19th century warfare. Raybin writes:
The rules (which have evolved over the last twenty years or so) were originally designed for conventions where players expected to be able to learn a game in under fifteen minutes and to start throwing dice almost immediately. Obviously, then, playability and fun are central to the rules. There is no strict ground or time scale. It is merely representational at best which, in truth, is all one can say about any wargame.