Iron Choirs is a skirmish game set in a fantasy post apocalyptic world. It’s a work in progress, but it is free right now at Wargame Vault. It could be of use.
skirmish
Most Irregular Horse and Musket Rules
Most Irregular is horse and musket rules extension to the Fast and Dirty skirmish rules, found on the same page.
Dying Star Oblivion Skirmish Quickstart Rules
Dying Star Oblivion is an skirmish game based on Samsun Lobe’s Dying Star series
Colonial Skirmish Rules
The Tyneside Wargames Club offers their free wargames rules for Colonial skirmishes.
Pot That Fellow, Somebody Colonial Rules
Pot that Fellow, Somebody is a set of free miniatures rules for the colonial era. Author RP Bergman writes:
These rules are intended to fight Colonial quasi-skirmish level games with multiple players and 2-3 units per players. Colonial players includes Europeans, Americans, and any other modern power with advanced military technology. Native players include includes Zulus, Dervishes, Pathans, etc. Units are rated according to Morale Quality, Melee Skill, and Firearms Skill. The Morale of units degrades as they lose leaders, take casualties, suffer from the heat, or fail to take action during the battle. Eventually, even the best unit may “run away” to live, fight (and die) another day. Units take a variable number of actions each turn, with the better quality troops having a higher chance of taking more actions.