Honor and Glory is a set of rules for the American Civil War for games where the smallest tactical unit is a regiment, which is represented by four bases. It’s playable in nearly all figure scales. Originally available on the Yahoo Groups, I have archived the files there because Yahoo Groups is shutting down.
Sandpit Showdown is a set of free wargames rules for backyard battles with army men in the Wild West and Civil War.
Pete Pellegrino has written a set of free miniature wargames rules called Damn The Torpedos. In the game, you customize your ironclad, and then take it out to fight in the Cvil War battle of Mobile Bay.
The Civil War in 30 Minutes is a matrix game designed by Matt Fritz to help his students understand the American Civil War. If you haven’t looked into matrix games, you will find that they are useful in running meaningful campaigns.
The Battle for Henry Hill is a simulation of the First Battle of Bull Run designed by Matt Fritz for his students. The rules include an order of battle and links to paper figures.