From Gettysburg Gamers: a set of free wargames rules for Wild West shootouts.
Rules: 20th Century
Vietnam Skirmish Rules
The Black Dog of Doom offers a set of free wargames rules for Vietnam Skirmishes.
The author writes:
This is a set of wargame rules for playing a middling size skirmish set in the American/Vietnam war. The rules were written for use with 20mm metal minis and have been used in that role a number of times.
As well as the figures and terrain, you will also need to supply some standard dice, a measuring stick, lots of tiddley winks and some crunched up balls of paper!
The rules feature the use of supressing fire which will pin all but the bravest of warriors. In game terms, supressing fire reduces the ability of the supressed to interfere with your plans.
Also included are some rules for handling vehicles and artillery fire, although these features are not expected be the focus of the game. In play each player will easily be able to handle 20-30 figures.
When Technology Meets Tradition Early 20th Century Rules
“When Technology Meets Tradition” is a set of rules for wargaming early modern warfare conflicts, roughly from 1895-1915. The emphasis of the author is on early World War I (1914-1915) but other period wars are also of interest, such as the Russo-Japanese War or the Boer wars. The rules are fast-play and focus on the problems faced by military tacticians during early modern warfare: when outdated linear tactics and love of the offensive ran head-on into lethal, accurate, and rapid firing weaponry.
Struggle Against Everything And Everybody
Alan Saunders offers Struggle Against Everything And Everybody, a set of free wargames rules for the Mexican Revolution of 1910 – 1920.
Red Hordes Russian Civil War Rules
Red Hordes is a set of free wargames rules for the Russian Vivil War. They’re similar to DBA/DBM.