Cold Steel is a set of free wargames rules for the period 1690 to 1950 offered by Historic Enterprises. The first release offers the basic rules, plus specific addendums for the Wars of Napoleon and the War of 1812. The nice thing about the rules is that they offer a flexible scale system, with each figure representing between 5 and 60 men. This should allow you to fight a wide variety of battles with the same rules set.
Fast Play Rules For The Seven Years War is a set of free wagames rules for mid 18th century games.
All The King’s Men is a set of horse-and-musket rules designed for 54mm figures.
8e Cuirassiers 1700 – 1870 is a set of free wargames rules for the horse and musket period. An infantry battalion is represented by four bases.