Dougi has a set of adaptations for solitaire play of the popular commercial set of rules Song of Blades and Heroes.
rules
The Square Brigadier Rules
The Square Brigadier is a set of horse-and-musket rules based on Bob Cordery’s Chess board game inspired by Joe Morschauser.
Battlelore Napoleonics
Battlelore Napoleonics are a set of adaptations of the Battlelore Fantasy/Medieval card driven miniatures/board game. I like the Battlelore system a lot.
Beware: this site has an obnoxious pop-up video ad embedded in it.
Pz8 Coastal Rules
Pz8 is a series of two-page wargames rules. Among them are is a set of free wargames rules for coastal actions.
Giant Stompy Robots Rules
Meca Tac – The Giant Stompy Robots Edition is a set of free wargames rules for Mecha battles.