Wargames Rules 1685-1845 is a set of classic WRG rules from 1977. I own a copy, but you can get your own in pdf form at the link.
Here’s an English Civil War variant of the Command and Colors rules. You’ll also need the Command and Colors: Napoleonics rules, which are freely available on the GMT Games website.
Daimyo is a set of free wargames rules for samurai battles in 15mm.
From the website:
Daimyo is a set of wargames rules intended for use with 15mm scale wargames figures but can easily be used with other scales (although I for one won’t be painting any 6mm samurai!). The rules cover the period known as The Age of the Country at War or Sengoku-Jidai. This was a period when samurai armies became much more organised, the importance of the ashigaru infantryman was recognised and the increasing use of firearms altered samurai warfare forever. It was also an age that produced some great commanders such as Oda Nobunaga, Toyotomo Hideyoshi, Takeda Shingen, Uesugi Kenshin and Tokugawa Ieyasu to name but a few. And, in a period of continual warfare, there were hundreds of battles, some of them epic encounters like Nagashino, Sekigahara and Kawanakajima. It is my hope that Daimyo will capture some of the excitement of this colourful and unique period of history
In the Jungle is an interesting set of rules for conquistador vs aztec games. It’s played on a gridded board and is supposed to simulate a group of “lost” conquistadors trying to find their way to a temple without falling victim to sacrifice.