Today you have atthe Warlord Games webshop three rulesets in free digital download. All three are worth it, so you know. The rules are:
Black Powder that includes a module for the 1st Carlist War 😀
Pike and Shoote, for the period of the English Civil War / 30 Years War 😀 😀
Hail Caesar for the ancient and medieval period.
The three rules share mechanics, but they are different and give “good feeling” of their historical period.