Andy Watkins offers a set of free wargames rules called Brigade Commander, for games set in Cold War Germany. Given the equipment used, I suppose it also would be useful for gaming some other scenarios in which the combatants have old NATO and Warsaw Pace equipment.
The War Times Journal offers a set of free Napoleonics miniatures rules called Republique.
The War Times Journal also offers orders of battle for Jena-Auerstadt, Waterloo, Busaco, Wagram and Dresden.
David Wareham offers a set of WW2 Rules For Brigade Level Games
The Battle of Blackburn’s Ford is an introduction to the Combat Command American Civil War Rules. The pdf also includes counters if you don’t have figures.
Over The Top is a set of free wargames rules for brigade level games set in the First World War.