The Savage Worlds role playing system has attracted the attention of a lot of miniature wargamers becuase it is so easily usable as a miniatures game. There’s even a free subset of the role playing rules called Savage Worlds Showdown, designed specifically for miniatures skirmish.
Here’s a free expansion for Savage Worlds for playing Lord of the Rings Skirmish Games.
John Armatys offers a set of free modern skirmish wargames rules called Fireteam II They’re designed for use with 20mm figures.
Sandpit Showdown is a set of free wargames rules for backyard battles with army men in the Wild West and Civil War.
Fire and Discipline was originally published (in 1988) to cover tactical warfare from 1740-1850. It is now in two versions, one focusing on firepower, the other on discipline. Both versions use the same basing and organization structure. The rules are lengthy because many simple questions are answered with the clarification examples. Optional rules are included to allow for more realistic and slower play for those who prefer it. After learning the rules most players will be able to play a friendly game by using only the pullout charts.
I have a large collection of 1/1200 Civil War Ironclads but have never played many games with them becuase I haven’t really found a set of rules I liked. I may give theis free set called Smoke on the Water a try.